Before trying something like the fuel pump idea, make sure that is the problem.
Has the cat been sitting for a long time? Don't run it that often? It sounds like it works OK on level stuff. I'd first of all check all the lines leading up to the pump for any blockage. I'd also check the fuel, diesel doesn't like to sit for long periods of time (it starts to pick up contaminates). I'm sure you've seen those huge filters for diesel motors - they have them for a very good reason. Diesel can also pick up a bacteria that is hard to eliminate. Have you used any fuel conditioners? Some of them work quite well at preventing/solving fuel problems. Does your tank have some sort of venting so that you aren't having a vacuum lockup?
Fuel injection (diesel) pumps have a low side, where the fuel is pumped from the tank to the injection pump, and a high side. You may have to have the low side checked out. Does your manual say anythhing about it?
