Look at your rear end pull the differential cover off lift up the rear axle inspect very carefully for good clearances to make sure the tires spin (in nuetral of course) make sure the ring gear isn't wedged into the pinion gear. also it certainly sounds like you cut your drive shaft too long perhaps, if so remove a little bit more and try again, dont forget to make sure the driveshaft is balanced and weighted you could do severe transmission damage if not possibly break the tail shaft housing and or tail shaft/planetary set