[Only Toyota for me]

I'm assuming you have a u-joint going bad from what it sounds like to me.

How well have you maintained this truck?

Do you grease the driveshaft at least every other oil change?
Has the transmission been serviced?
Diff fluids changed?

Some of this stuff should be done according to TIME or mileage, so even though you have low miles it should still be done. Your truck is 5 years old now, which puts you in the 60k mile towing schedule.