LX90

My car's in the shop right now having the 4.10s installed. Well, we put in the new pinion gear, back spaced it according to specs, and torqued it down per Motives directions. The pinion gear is tough to spin by hand, and when we put the carrier (differ and ring gear) on and shimmed it, you cannot spin the rear end by hand at all. Does anyone have any thought's at all as to why? We're gonna pull it all apart tomorrow and see if something shifted or what ever may have happened. Any thoughts to help would be greatly appreciated. Thanks.