[twinmill28]

H40 is a great forum for H2 drive train knowledge, Zach (who I think is a member here but does not frequent much) has a built H2 and is a GM parts guy, so he can get you info and parts to make it work. Zach and I have been swapping parts from left coast to right coast for a few years now and is a great guy to deal with.
There's also a Blazer guy on H40 that has transplanted a diesel into his truck and has BUCKET LOADS of knowledge on everything mechanical, including the HUMMER's.
It's a smaller H2 crowd over there, but the guys know their deuces.
Also, H4O brought a HUMMER mechanic into the forums and has an "Ask Mike" section to post up HUMMER related problems, so that's a good source of info as well.
Yeah, they're H3 heavy there, but still a great group of guys who love the hobby as well as and possibly more than us.

Unfortunately HUMMER Forums seems to be on life support, sad to say because it has the most logical name for a HUMMER forum.
HUMMER X Club is another one that's been around for awhile and has some die hard members, but has gotten slow over the years.

I like to surf across several of the forums for different HUMMER needs--Elcova has always been the best for me to sell any H2 parts I had, lots of good people on here.