blueflamed03
Supporting Member
no to TB spacer, gears and tune 
i want more power
- Thread starter johnny_nap
- Start date
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
A big NO on the throttle body spacer... those only helped the old carbed and TBI engines since they allowed better fuel atomization. They do SQUAT for port injection like ours since the fuel is metered right at the intake valve through a high pressure injector.
GT4's are 3.73s and you should've had 30.6" tires stock, to get that same gear/rpm/mph relationship with 35s you need to install 4.30s (it's almost exact to the 1st decimal point). It'll put you back to stock shift points and allow you to cruise at the original ~2150rpm at 75mph.
If you want some more grunt, move up to 4.56s, which is about like having 4.10s with the stock 30.6" tires. You'll cruise 75mph at around 2300-2350rpm. This might be your best option with those heavy 35s.
From here you can get long tube headers and full exhaust. Get a tune after you get everything done since then the tune can be tailored to give you the most gains from those mods. It makes a pretty big difference on the 5.3s. You should be around 330-340hp at the crank with these mods on a 5.3.
You can get a supercharger. Get a positive displacement supercharger since these are trucks and need lots of boost down low. This quite an expensive option and you do risk damage to the engine. Without forged pistons, even one hiccup from an injector and a piston goes toast.
Most people will tell you to check the salvage yards and pick up a 2001+ LQ4 or LQ9 and swap it in. It's very easy since everything matches up, all you need is a tune. You should be able to pick up a good 50-80k mile 6.0 for under $1500. I see them in my local salvage yards for less than $1000 all the time. They are a strong engine even stock.
An LQ4 with intake, full exhaust, and a tune will be around 380hp at the crank with a much more broad torque curve than a comparable 5.3.
