Joe & John:
That is one of the issues with the system. ABS triggering when you don't want/need it to. TT4 seems to work OK on high traction areas like Moab, etc. Over here where we have mud, loose dirt, gravel, not as well. There were several times over our New years trips where the TT4 trucks could not climb obstacles that the old ones did fairly easily. Driver experience wasn't an issue. Complexity is another issue. I have seem TT4 fail numerous times on the trail for one reason or another, usually due to a sensor that has shifted or become caked with dirt. When that happens, you can still BTM, but it is not nearly as effective as the old trucks because of design differences in the differential carrier. Check the Hummer Info Database on humvee.net for more technical info.
That being said, BTM has it's drawbacks as well. Increased brake wear, increased strain on the driveline, still not 100% as capable as a locker.
Many BTMers will say that BTM has gotten them through most every obstacle they wanted to cross, but everyone I know that has put lockers in (including myself) hasn't regretted it.
Scot Smith
1994 HMC4, Locked
"They're right, Wider IS Better..."
Southern Axle & SteeringRemanufactured Driveline & Steering Parts for Hummers