2003 Gmc Towing Performance Boost

twa767 · August 23, 2011

2003 GMC Sierra 1500. Extended cab short bed. 4.8L V8, auto trans and 3.73 gear posi rear end. It came new with the factory installed towing package. I bought this thing new and have always run Mobil 1 oil. 67,400 miles currently. The only modification I have done is install a cold air intake. My max towing capacity with this setup is about 6700 lbs. Just bought a travel trailer that will gross out after being loaded at about 4500 lbs. Well within my truck's ability. My question to everyone: What would be your suggestions to develop a little more power? I not talking internal modifications to the engine. Won't go there. I have had suggestions from friends of running dual exhaust, headers, performance chips (do they really work?) and so on. Any suggestions and thoughts are appreciated. I know my truck is ok pulling this trailer just trying on making it a little easier for it. Current tire size P265/70R17.

Stevens03 · August 23, 2011

Gear swap would be my number 1 thing to change. If your running the stock tire size, 4.10's will work great but if your running a larger size, I wouldn't be afraid to run 4.56's. Next would be long tube headers and a custom tune.

And Welcome to the site

nickvrebel · August 23, 2011

From experience:

*a 4.8L with 3.73 will tow <5,000 lbs all day without an issue as long as you aren't getting in to the mountains.

*don't waste money on a programmer, any gains will be negligible.

*headers and open exhaust will only hurt you. While it can increase horsepower on the top end it lowers torque on the low end, and the 4.8L is already hurting on torque, you don't need to make it worse - you NEED torque.

Honestly the best and cheapest thing to do would be to swap in a 5.3L You could pick up a used low mile 5.3 for ~$500 and it can be swapped in with one or two mechanically inclined friends in 1-2 days depending on how hard you work and how much you know. It's a direct swap.

APT · August 25, 2011

For that low mileage, 4.56 gears.

Stevens03 · August 25, 2011

I wouldn't run 4.56's unless you plan on running 285's or larger.

wavery · August 25, 2011

I have a 4.8 with 3.23 gears. I tow a 4K# (low profile) trailer and a truck load of stuff. I regularly tow the trailer to 8,000' in the high Sierras and have no problems.

The only issue that I have is that if I am climbing a steep grade, I have to put it in 2nd and increase my speed to ~65MPH (@3600RPM) to maintain the torque necessary to climb the grade without slowing. There is about 4-5 places in the entire 350 mile trip that I have to do that and it's for about 5 minutes on each grade. 25 minutes out of a 7 hour trip surely isn't worth changing anything (for me).

I just leave it in 3rd, set the cruise and let it go. When I see a grade ahead, I take it out of cruise, increase my speed a bit (68MPH tops) and usually make it to the top without shifting to 2nd. If it's a long grade, as soon as it ges to 2nd, I shift to 2nd and leave the cruise set @ 65.

I would LOVE to have your 3.73s, only because I could climb any grade without having to break the speed limit.

If you go to 4.11s you will increase your RPM and have better torque at lower speeds. You will also increase the engine wear over the life of the engine. If you go to 4.56, you will be running at awfully high RPM during normal driving and your MPG will go down. However, you would be able to pull a house.

I just can't see sacrificing MPG and engine wear for the small % of time that you may benefit from having lower gears.

Personally........ I would sell the truck and buy the one that I want before doing an engine swap. That's asking for a world of problems.

music · August 25, 2011

Don't change a thing, other than maybe your expectations. Stick to 3rd for pulling, and 2nd for climbing. I know from experience, you can run in 2nd gear up steep grades for hours without issue (ask me how I know), but you won't usually need to. You'll find that 3rd will keep you going over most terrain. If you use cruise, it may shift to 2nd too easily, but it doesn't hurt. If you use the right foot instead, you just let it slow down a little instead of shifting.