vibration help???

so when im accelerating in 1st n 2nd gear im getting this very strong but unusual vibration. my brother who is very mechanically inclined seems to think its a driveshaft issue so i greased my u-joints and it helped for a little while (at least i think so) but now its back. only happens at certain rpms. has anyone had this happen to em or heard of this. and whats yalls opinion on it being a driveshaft issue.

 

Sounds like you are on track, have you noticed any play in the u-joints while you were under there greasing them? How many miles on the truck, what year?
Get under there, with both hands and push and pull on the driveshaft at the joint, usually you can see the play.

 

common problem. First things to check is the U-joints, carrier (center)bearing. Get that 100% and then you know if you need to go further into the wheel bearings.