Originally Posted by OldWoodsDiesel

well, i'm in PA, so not much help to you. you can probably find one in a junkyard for a couple hundred bucks though - maybe less. your t-case (BW1356) should be on every 4x4 F-250, F-250 and F-superduty from like 1987 (or maybe earlier) through 95. and gas/diesel, smallblock/bigblock doesn't matter. it'll take half a day and lots of swearing to get out of a u-pull-it yard, but you'll have your question answered...

your problem only happening in higher gears makes sense, though - in those gears, there's more 'leverage' from the rear end on the engine (through the trans and t-case) than in lower gears. so where the offending gears/bearings can hold on in 1 and 2 (and probably reverse), they can't at higher gears. keep driving it and itll start doing it all gears eventually...

however, doing it in 4th gear means it is almost certainly the t-case, as in 4th gear, the ZF trans essentially just locks the input shaft to the output shaft, thus the opportunity for gear slippage is minimal. so my money is on a worn t-case, for what its worth...