Thanks Gene, After a month I am getting to know just what you have said.
I think, (but I can't see enough to do anything about it), is that (as Spock would say) the only logical thing is if it works out of the tank and not in the tank than it must be tank/float interference.
The arms and float location are a bit different on the new pump. I had shortened the arm on the old pump so might try that arm on the new pump.
I also have a bore-scope camera and if the above doesn't work I could drill a small plug-able hole in the top of the tank.
I have drained and partly refilled the tank once but it's a ugly job. The Jeep tank has a small molded recess in the bottom (?) and the Dakota pump when installed is very compressed (Grasping here).
Thanks. I will post when I know anything new.