Sounds like your control trac is having issues. There are sensors on the
front and rear driveshafts which tell the computer how fast they are spinning.
If the rear driveshaft speed goes faster than the front, then the GEM will
tell the transfer case to engage the front axle more - it can vary from 10%
or so up to 100%.
If your front axle is over engaging, then that will cause windup tension in
the front axle. That tension can be "slipped" off by the front tires
slipping a little, or it can be released with a thump or bang - usually the
transfer case clutches slipping all of a sudden.
If its the control trac, you will not get this bang on a dirt road as the
tires can slip off the tension.
The most common issue is old dirty sensors - you can pull them out and clean
them, and check them to see if they are still good.
Hope that helps!
Message posted via http://www.carkb.com