every 3rd tank full I add 12 oz of sea foam.before I fuel up, I buy it in a gallon can from Amazon, available in 12oz cans at wal-mart, it makes the truck run fantastic, speed, idle, take-off, mileage, and overall performance for my 2004 H2 with 223,000 miles on it…..I tried intake,exhaust,speed chips, outside of a lot of noise, no real improvement. And wasn’t going to to put a blower on it, went back to all stock, and Sea Foam….no complaints

2004H2
2006H3

 

I did have the transmission rebuilt, to Corvette status, heavy duty parts, longer shifting intervals, costs $500 more but it was worth it……from romp-down to 80 mph,your there in no time…..with 37” Toyo M/T’s


2004H2
2006H3

 

[QUOTE=guptas;412750]As a relatively new and younger Hummer owner, what is the best way to increase the speed on a 2003 H2 model? I have to take it into the shop either way to fix some issues regarding steering and whatnot but was considering supercharging it along with adding a magnaflow exhaust, thoughts?[/QUOTE

Regaining lost HP should be #1 priority.
Clean mass air flow.
Front back of throttle body
New spark plugs
coil packs
dellhi fuel pump
replace the belts

installing corvete servo on side of trans is huge. The issue of acceleration on on ramps will no longer be a problem
eventually you get the vehicle tuned by blackbear.

 

Very few things are as effective when it comes to increasing the HP/Torque of an H2 then a supercharger.

The LQ4 is a great candidate for it, the bottom end and cast iron block is bulletproof and if in good condition lends itself well to supercharging. If you purchase a magnuson SC use the tune they send with it, It will be specific to your parameters and provide great results.

Replacing the other items you mentioned will also help. Make sure the transfer case is up to the task and that the chain is not stretched out or you might have problems there. If its a high mileage H2 check the U-joints and half shafts as well.