Stupid question, hoping for help

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Alex33

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Hi all, I have a new to me 2001 suburban, 4wd w/ a 6ish" lift and 35" tall tires. According to the PO the truck has 4.56 gears installed at the front and rear axles. It runs great around town but feels a bit sluggish going uphill. I was going up the pass out here and the truck would not go above 55mph. It felt like it was in overdrive the entire time. I shifted to from D to 3 and nothing changed. Any suggestions on where to start looking?
 

Erickk120

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I mean 35's and a 6 inch lift, and depending on the slope of the hill I wouldn't be surprised if it felt like a pig.
 

dnt1010

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The 4.56 should help a lot with the oversize tires, what rpm are you seeing at 55 mph? What engine?
 
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Alex33

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The 4.56 should help a lot with the oversize tires, what rpm are you seeing at 55 mph? What engine?
It has the 5.3. Rpms wouldn't go above 2500, that's what really concerned me.
 

dnt1010

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The early 2000's version of the 5.3 if healthy should provide around 285hp which is more than enough to move even a 6500lb burb up a slight incline at a good clip. (not ever going to be considered fast LOL) Very concerning that you are not getting a engine rev above 2500................................ I am not sure how your local laws are on emissions testing are? but if this were mine my first stop would be to drive over to my local trusted exhaust shop and have the catalytic converter cut out and a "test" pipe (Haha) welded back in. I have seen numerous vehicles of every make and model that exhibit low power/low rev due to a severe exhaust restriction. Most of the time you will get distinct engine moan sound on a severely restricted system. It is quite distinct and once you have heard it a few times you will readily recognize it. On a lifted truck running oversize mudders your problem may be that you cannot hear it if the tires at each corner are howling like wild dogs LOL. Anyway it could be several different things but from past experience I suspect a catalytic converter.
 
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Alex33

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The early 2000's version of the 5.3 if healthy should provide around 285hp which is more than enough to move even a 6500lb burb up a slight incline at a good clip. (not ever going to be considered fast LOL) Very concerning that you are not getting a engine rev above 2500................................ I am not sure how your local laws are on emissions testing are? but if this were mine my first stop would be to drive over to my local trusted exhaust shop and have the catalytic converter cut out and a "test" pipe (Haha) welded back in. I have seen numerous vehicles of every make and model that exhibit low power/low rev due to a severe exhaust restriction. Most of the time you will get distinct engine moan sound on a severely restricted system. It is quite distinct and once you have heard it a few times you will readily recognize it. On a lifted truck running oversize mudders your problem may be that you cannot hear it if the tires at each corner are howling like wild dogs LOL. Anyway it could be several different things but from past experience I suspect a catalytic converter.
Thanks for the reply. It passes smog pretty easily so I would think the cats are ok. I've goosed it around town to see if I could get it above 3500 and it does. It could just be that I'm doing something wrong too. I could be pretty lazy on the gas with my old car and it ran up anything easily. This is a while different beast.
 

dnt1010

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  • Yes it might just be unfamiliarity with the engine/trans/gearing combo?. The 5.3 last 1" of gas pedal travel should force a trans gear kick down to get the revs into max torque HP range regardless of gearing. Take her out and make a few full throttle passes..
  • I would guess that the max torque is in the low 4000 rpm and maximum HP is in the mid 5000 rpm range. You can find exact info for your year model and engine with a google search. That should get you moving in the right direction. Most of the 5.3 engines are weak at low rpms, the torque only starts to build above 2500 rpm range. Now of course on an older used vehicle you never know what has been done to it, so you could have a trans or torque converter issue (lets hope not)
 

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