Where is it exactly, i.e. under the engine (left/right), under the rear axle, etc. Also, is it exactly clear? Oily? Greenish? I will presume it is water.....
Possibilities:
1) A/C - there are drip tubes for condensate for both the front and rear (if you have it) evaporator units. The front drip tube is on the front right (passenger side) under the fan. The rear drip tube is by the rear left wheel.
2) Exhaust - The engine makes water as part of combustion. To allow the condensed water to get out of the exhaust system, there is a small hole in the muffler, so the drip will be on the right side kinda in the middle of the truck, and there should be another right under the exit of the tailpipe.
Hope this helps.