So found a deal on marketplace for some 38x15.50R20 with a super negative offset and picked them up! Was pretty stoked that most of the rubbing was on fiberglass. Cut out everything around the firewall trimmed the fenders and slid the flare back. Looks factory!! Hard to tell in picks but changed the whole truck. Low and wide love the look! Down side is it robbed what little power the truck had lol. Have pulled and built diffs in a few older Toyotas. But can’t really find any walk thru or vids on doing a gear swap in an H2. Will be towing a boat so thinking some gear range around a 5.10. If some could help lead me in the direction on what axel is factory in this 05, is there a factory locker I need to be worried about? Also annyone sell a rear differential with 5.10 gears already in it?Any info on someone doing this would really appreciate it! Just doing the rear for now. It’s my daily so hopefully can do the rear in a weekend then do the front the following. Understand not to use 4x4 until it’s the same ratio

 

truck is all the time 4WD so you'll need to do both front and rear at the same time.
I did 4:56's in mine with true 37" tires and due to the 6L trans double OD. I think 4:56's or 4:88's would be good with the 4L trans. you have a .70 OD which is a little better than mine at .667
If I remember correctly yours has the same 14 bolt semi-floater 9.5" in the rear and the 9.25" IFS in the front as all other H2's had.
from when I did mine, https://www.hummerforums.com/forum/h...-4-56-a-48469/

Neal

 

Wow you just saved me!! Would have just tore my trans up thank you!!

 

5.10 or 5.13 would be too much. I would recommend 4.88s with the 4l65 trans especially if you're towing.

The 6l80 has a .667 6th gear. 4l65 has a .70 in 4th gear. You will turn more rpms in top gear with a 4l than a 6l with the same gear ratio. With a truck of this weight and towing, you'll be perfect at 4.88s with the 4l65.

And yes, your transmission will destroy itself shortly if you don't gear down.