Vibration when driving 25 MPH?

Check the tire balance first then check the front end of anything worn out or loose. You say it starts around 25, does the vibration get worse when you go faster

The faster you go it gets a little smother and sometimes when I shift to reverse or drive I hear a clucking sound more to the rear of the truck.

Do you feel the vibration in the steering wheel? If so check the front end for balance. I wonder when you put it in reverse it clunks, This is what I would do if it was my truck. Jack the back up so the wheels are off the ground and it in neutral, turn each wheel to see if there is play anywhere. check the fluid in the diferental. If all seems good check the universals. if they start to go bad they will make a clunking sound. I had it happen to me and I did not think it was anything until my driveshaft fell off.