Propeller Shaft UJoint

[denvern]

Does anyone know what causes the ujoints to wear on the driveshaft from the transfer case to the front?

I have a 2004 with 50,000 miles and lately have experienced a slight vibration while accelerating with the allmode 4wd. It was diagnosed as worn ujoints.

The previous owner did tow something with the truck could this be the cause?

I just think its a little premature for those parts to have worn out.