It sounds very similar to the problem I'm having. In my case I suspect that the settings on the pump is incorrect, thus the governer kicks in when it's not supposed to.

The other, which I still have to look at, is a leak on the fuel line between the pump and the tank.

The fact that your smoking increases, indicates that either your engine is not getting the air, thus the mixture is more rich, or calibration on the pump that is out.

It could also be that one of the solenoids on the pump does not open up properly when it's hot, due to heat expansion.

'99 Isuzu Frontier (Rodeo) Intercooled 280DT LX