90 4x4 diff ???'s

I have a v6 toyota and need a little help my pinion bolt came loose one day some how while going down the road and started vibrating real bad so i tightend it down but mabie to tight because it went away for a couple of days but started again so i checked the diff. by rocking the drive shaft and it had some play about a 1/4 inch back and to so i took the diff out to check it and it seemed fine the 1/4 inch wasnt there and the axle splines didnt look bad any ideas???? one wheel bearing was bad but i dont think it would cause that much play oh yea i couldnt turn the diff by hand when i took it out but i did impact the pinion bolt down to so i backed it off and it spun fine

A little play is normal, esp in a 20 yr old truck.
There is a specific torque value for the pinion nut, which i can't think of right now.