I have a 1999 Chevy Tahoe with a rancho 6" lift, stock drive shaft with 36" tires. I was wondering what caused the trasfer case to crack after a year? I replaced it with a used transfer case less than a year ago with about 800 miles on it afte it cracked again. The macanic I took it to ( that dose not know too much about lifted trucks) said the stock drive shaft I have needed to be modified to fit the 6" lifed that it was viberating too much and that's what caused it to crack. The truck has been lifted for years and all in the sudden it has been giving me problems. He wants to charge me $1800 to have that transfer case replaced AGAIN, the drivshaft modifed and instalation. Has anybody had this probelm before?? What do you think I should do?????  

it should have a sye and a cv drive shaft, it'll get rid of the vibration, and quit wiping out the extention housing bushing and seals. the used one may have taken a few years of abuse before you got it.  

Have your driving habits changed at all recently? Been jumping the truck?