Can you guys help me out - I have a problem. Have a 1991 GMC K2500, 3/4 ton, 5.7. Put a new GM crate motor in and it overheats. Does the water pump have to be a reverse pump because of the serpentine belt set up? It overheats under a load, but does fine sitting in the garage idling. Has a new thermostat and new radiator. Any ideas?