80,000 miles cracked transmission,transfer case and rear end out.radiator last

Humm, Hummer been doing any off-roading? Just easy street miles i guess. Buy it new or used?

is it the mounting flange for the tranny that is cracked? probably had micro crack to begin with. gradually get worse with time. you would need microscope to see initial crack. there is a bushing inside the output seal and bearing that will wear with time. as it wears, allows drive shaft movement which can trickle in to other components(output bearing, output seal, u joints, etc). is just possible. something a person wouldn't think about. that bushing can't found at dealership either(even they have to order it from aftermarket shop). vibration in shaft can effect the rest of the drive train.