annoying vibration

hey guys. just seeing if any of you knowledgeable people on here know what the heck is going on with my truck.

2000 toyota tacoma
reg cab short box
2.7L
5 speed
3 inch coil spacer and chev half ton rear leafs for a 3 inch lift
31" bfg all terrains

there is a vibration on the highway. anything over 80. i know what wheel unbalance feels like and this certainly is not it. its not in the steering wheel, its just the whole truck, the seat and everything, it feels like im in a vibrating massage chair on wheels. no this doesn't bother me that much but its just annoying and doesn't ride smooth like my other trucks have. just seeing if you guys have any ideas of what might be going on... wheel bearing? u-joint? etc. one wheel bearing has been replace by previous owner just before i bought it if that helps.

thanks
brett

 

thats what i was thinking but there dosen't seam to be any play it just seams to move a tiny bit but when i look the rear pinion is moving to. so i dunno.

 

hmm. ill have a closer look and if i still don't find anything ill take the shaft out. not that hard, as long as it stays warm for a bit

thanks
brett

 

o yea sorry i always forget about the americans on here which really is a lot lol. the trucks form the states to so its all in mph but i still look at the kms/h

 

would that make the whole truck vibrate on the highway though? and i noticed tonight it wasnt quite as bad as earlier but it still does it. its mainly around 110 km/h to 120 km/h