it is going to be 1 of 2 things then if it idles fine around town.
I have never used an electric pump, but it is possible.

But my bet is the fans and the fan shroud.

Put a cut off switch to the power to the fans. Once you are up to speed turn them off. I Bet it cools down just fine after that.

The solution if that is the case, is to cut some flaps into the shroud, that are hinged. Feets showed me that when we used the maxima fans. You cut out some rectangular holes into the shroud and then hang flaps over to cover them.
At idle, they get sucked shut, at speed, the blow open to alllow more air flow.