I have an '85 2.8L 4x4 that's losing power as I drive. There's a couple of things you first need to know.

1- Truck was parked in a field for 9 years before I started working on it
2- Engine misfires with the odd pop (fuel delivery problem?)
3- All filters, spark plugs, and spark plug wires are new

When I drive, I need to continually pump the accelerator to maintain a driving speed (100 kmh/60 mph). If I do not pump the accelerator, the engine will slowly die out, and I'll need to downshift. Would it possibly be my fuel pump? Its only the one cylinder that misfires.

Sounds like the venturi are plugged, and the accelerator pump is the only thing giving the engine any gas. rebuild the carb or clean it real good.

Well, if I'm going to rebuild the carb, maybe I'll rebuild the engine as well :(. I want to restore this truck, but the plan is to do it when I have a house/driveway/garage to work in.

Any suggestions on where I could buy a new or better or used one instead?

well, if you're into the effort involved, i'm pretty sure the 2.9 would bolt up to the same transmission as the 2.8, you could just do an engine swap and drop in the computer and wiring harness for the 2.9.