I recently purchased a 99 GMC K2500 Burb, 454, 4L80e. Bought it with 270k miles, changed out the trashed transfer case, new brake suite up front, battery, plugs, wires, oil change. Runs great, engine starts and runs like warm honey.
It does run rich, and if I romp the gas down, it stalls out and takes a minute to restart?
Is there any suggestions high mileage people have for me? This is going to turn into a camper truck, so any experienced advice would be appreciated.

 

O2 sensors, the ones closest to the engine should be changed when plugs are changed. They wear out and get slow affecting fuel mileage. Fuel filter is a common neglected item also.