Will 5.3 to 6.0 (LQ4) make a big difference in towing?

[Teamwieland]

My 2003 Suburban with 5.3L has 225k and I just upgraded my boat. 3.73 rear axle. Boat is about 6500 lbs on trailer. Love my Suburban but at 6000 ft elevation I lose about 30% of my power. 5.3L struggles bad with the new boat, especially on hot days and loaded down. Looking at dropping in an LQ4 (salvage or reman) if it will make a significant difference. Not willing to go LQ9 as 85 octane is expensive enough. I know fuel economy will fall off a cliff as my folks have a Silverado 2500 with LQ4, but I'm mainly trying to avoid buying a new truck altogether. Anyone done an LQ4 swap for improved towing?
Also,I bought a 2013 Tahoe this year with the Gen IV 5.3L. After CAI, straight through exhaust, and Diablosport tune, it didn't tow any better than my old Suburban. 5.3 isn't the answer for me at this elevation.

 

[Teamwieland]

Forgot to mention I bought a 2013 Tahoe this year with the Gen IV 5.3L. After CAI, straight through exhaust, and Diablosport tune, it didn't tow any better than my old Suburban. 5.3 isn't the answer for me at this elevation.

 

[S33k3r]

Honestly, since you are losing power at higher elevation, you should add a turbo with very minimal boost. Why? because the turbo will maintain air pressure at altitude. Also, with minimal pressure, you aren't going to nuke your engine. You might even see a little mpg gain.

 

[Scottydoggs]

i used to have a 03 gmc 2500hd pick up, towed my 4,000 lb boat every where with no issues, hardly knew it was back there. im going to have to say gears would be the fix. i had stock 4.10 gears. my 03 6.0 had under 300 crank hp. these newer 5.3 have more hp and tq. you'll just need a tune after a gear swap to keep the speedo reading right, front and rear gears if a 4x4.

 

[Teamwieland]

If I get a new(er) truck it will definitely be boosted, whether diesel or ecoboost. Sticker shock is keeping me from pulling the trigger and I love my old Burb. Any recommendations for a turbo or supercharger?

 

[THarber]

6.0 is going to be better but I think you'd be better off adding a whipple or supercharger. Turbo is a lot more work.

Tim

 

[Bill 1960]

LQ4 will get it done based on my experience towing fifth wheel trailers in the mountains. However the 4L60e won’t be up to it. Better anticipate a trans too.

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum.

 

[Teamwieland]

Supercharger is about $6k and my Suburban is worth about $3k so probably won’t go that route. i think I will look for an LQ4 with low miles and freshen up the gaskets and such and see how it goes. Did the 6.0 vehicles come with something other than the 4L60E?

 

[S33k3r]

Yes. The Denalis and Cadillacs came with 4L65es. I assume you are going to do your own work, in terms of the engine swap? I misunderstood, previously, and figured if you were paying to have it done that would be the better route.

 

[Teamwieland]

guessing 4L65es are a little more stout. Since I’m losing 30% of my power here in Colorado maybe a LQ9 will get me close to what a 5.3 has at sea level and the 4L60 will be fine. Thanks for the great info.

 

[adventurenali92]

I tow with an LQ4 in my 2006 Denali xl and I also live in the mountains. Town sits at about 7,000 feet in elevation. While my towing has not gone over about 4500lbs, my LQ4 and my rebuilt 4L65E trans handle the boat I haul up and down the mountain roads for a close family friend, pretty easily. I’m not necessarily winning any speed races going up the grades when I’m towing but it pulls and pulls and pulls faithfully and doesn’t struggle. All I’ve done under the hood is a spectre intake, and a mild magnaflow muffler in pace of the factory muffler, and had blackbear performance do a tune. That’s a piece of the puzzle I would absolutely recommend. He tweaked a lot and adjusted for being at altitude most of the time. Here’s what I tow most often behind my Denali.

 

[Sam Harris]

Honestly, since you are losing power at higher elevation, you should add a turbo with very minimal boost. Why? because the turbo will maintain air pressure at altitude. Also, with minimal pressure, you aren't going to nuke your engine. You might even see a little mpg gain.

I’ve actually heard it would be better to add a supercharger at higher altitude, since it doesn’t depend so heavily on air density to accomplish the increase in power. Obviously, the higher altitude means less O2 content.

 

[Sam Harris]

What kind of altitude are we talking about? I appreciate the feedback from @adventurenali92 , but to be honest, the mountains in Ca. altitude are a whole different ballgame. We start out at 5280, and go up from there (5,861 here in my town). Once you head to the mountains, we’re usually at 10k+ pretty quickly. So I think that’s a pretty important piece to the puzzle.

From a quick glance, I’d say gears are the cheapest, most effective option to make a dramatic difference. Not that I don’t also want to swap an LQ4 in my ride…

 

[adventurenali92]

What kind of altitude are we talking about? I appreciate the feedback from @adventurenali92 , but to be honest, the mountains in Ca. altitude are a whole different ballgame. We start out at 5280, and go up from there (5,861 here in my town). Once you head to the mountains, we’re usually at 10k+ pretty quickly. So I think that’s a pretty important piece to the puzzle.

From a quick glance, I’d say gears are the cheapest, most effective option to make a dramatic difference. Not that I don’t also want to swap an LQ4 in my ride…

San Bernardino, which sits at the base of the mountains I live in sits at roughly 1,000 feet in elevation where you have to drive through at least coming from Orange County and Los Angeles to get up here. On highway 38 which is the highway I always take, what we refer to as “the backside of the mountain” actually takes us up to about 8000 feet elevation and then you drop back into town at about 7,000 feet. So it’s not like our mountains are small….. you see 7,000 elevation gain in about 50ish miles of driving.

 

[rockola1971]

I own (2) 03 Tahoe 5.3L 4wd and a 05 Denali 6.0L. The difference between the 5.3L and 6.0L is day and night. The 6.0L is a beast. I would go with the 6.0L and have a cam specd by a manufacturer for your needs. Port heads and custom exhaust.

 

[Alex_M]

How many miles on your 4l60e? '65 is not a much better story. The most noteworthy difference is the 5 pinion planetary gears, and the planetary gears are not going to be his failure point. The only meaningful trans upgrade would be a 4l80e, and that is pretty involved. Not worth the time for this kind of build.

If it were me I'd just do a Transgo shift kit, HD separator plate, and block off the accumulator in the case. All that can be done with the trans in the truck by simply dropping the pan and the valve body. Corvette servo would also help. Firm up your 1-2 shifts.

Your '60, if it's in decent shape, should last quite a while with just these changes. To me when you can throw $100 worth of parts at it to make it more robust, a trans swap isn't worth the trouble. Whenever you burn it up you can swap all these parts right over to another '60, or rebuild you existing one and make a couple more upgrades while you've got it apart. Raybestos high energy clutch set, z pack for the 3-4 clutches, .500 boost valve in the pump, wide apply band. I've got a lot of time towing behind a '60 built just like this and it has performed exceptionally.

 

[Fjs0001]

Maybe you could find a 2500 Suburban with the 6.0/4l80e and sell your old one? I almost went this route, but I really didn't want the length of a Suburban. If you're not going to add a turbo or supercharger, then go with a LQ9 for MO POWA!. I use 87 octane unless I'm towing something.

I think finding a used axle with 4.10 gears would be your best option. If I was paying for a gear swap, I'd go as low as 4.56 or 4.88? My friend had two farm trucks, a 2001 LQ4 with 4.10s and another 2005 LQ9 with 3.73s. He always said the 2001 with the lower gears towed much better.

If you do a motor swap, I'd looked for a 6.0/4l80e/transfer case combo. You could swap the motor until your transmission gives out. While the 4l60e is working you can figure out what all goes into upgrading to a 4l80e. It's really not too bad.

I made my 4l65e last as long as I could by adding a larger trans cooler, corvette servo, and the 3rd to OD upgraded servo. Whenever I'd tow, I'd let off the throttle and downshift to 3rd before going up a hill. I kept reading stories that the OD to 3rd downshift while towing destroys that transmission.

 

[MassHoe04]

Maybe a 2500 Suburban or Silverado might be a better match? Ready to go with bigger engine options and geared for heavier tow/pay loads.
Probably cheaper than trying to swap out engine, tranny and re-gearing.
That is what I would be looking into.

 

[S33k3r]

At which point adding forced induction is equivalent or even cheaper.