A 2.5/4 drop should be ok with a split shaft....
Biggest issue I have come across with center bearing failures is incorrect setup of the mount bolts...or the shaft is bottoming out in end of trans...
The center bearing carrier bolts should be loosely installed finger tight. The truck MUST be on all wheels and the rear suspension should be bounced up and down a few times....
Only then should the center bearing bolts be fully tightened...
There are also several aftermarket center bearing carriers available that seem to be more reliable than the stock units.
Finally, the rear shock angle changes substantially with a 4 drop...and raer shock relocation kits should be used to correct the shock angle...too much rear end bouncing around on a bad shock angle truck is sure death to a carrier bearing...
