[Wavery]

Did you check the pump strainer screen? It should be just on the inside of the pump intake side. It's just a little round wire screen.

I had a similar problem on my 2002 Coleman PU. The screen was completely clogged. I took it out, back flushed it and all was good with the world.

The other thing could be, if the pump is mounted higher than the water level in the tank, it could be sucking air from a pin hole in a hose.