well, let me throw out some thoughts. I have an 01 TT4/ABS truck and off-road a lot.
I do not believe it is possible to swap diffs, at least without a great deal of expensive and effort that would certainly make in pointless. The best option as mentioned is installing lockers to enhance the capabilities off-road. There are several options. I have been waiting to see if the eaton e-locker becomes available as an aftermarket kit. Hasn't happened yet. This is probably the best solution to improve capability of a TT4 truck
As for the ABS. Not sure about pulling the fuse. The question always is does the ABS fuse also power "other" functions that are critical. The real issue with ABS is on step declines where sliding off a ledge or like presents an issue. I for one have only had the ABS become an issue once on a hill decline. I stopped in plenty of time but it is a very un-nerving experience. Depending on where you wheel the ABS issue may never be an issue. Most of the concerns I've seen are from the folks in the Western States where steep decents are common. In the east is comes up but not often as an issue.
Bottom line is I would explore the locker option and think you will find your truck more than capable to meet all challenges.
2001 H1 Opentop
Former 03 H2 Adventure Series
Homepage:
http://www.hummerh1.net