Just some quick advise if you decide to replace the Pump. If you have a somewhat level Grassy area you can pull your truck on then do the job there.
Take the bed off. Don't drop the tank. I did it myself by removing the 8 main bolts, tail lights and unclipped the wiring harnes from the bed.
Once loose from the frame, just slide the bed towards the driver side. The bed will move sisde to side much easier than foward to aft. allow the bed to drop to the (grassy) ground and walk it up on its side then all the way over till it sits upside down next to your truck.
It's a breeze. I did the whole job in 2 1/2 Hrs by myself....Good luck!