So.. I drove down and filled the tank, even though I had a few gallons left (gas was sloshing, the gas gauge does not work)... On a full tank it runs great. That means that the pickup tube is messed up, or that there is crap in the tank. I have a new sending unit that should solve most of the problem, but if I don't get the tank cleaned the problem will come back.

- So it's off to the radiator shop to have it cleaned out.

thanks for all your input guys.

Stupid like a fox.