I have a 96 GMC sierra that had a 4.3 vortec but it bent a rod so I did a 5.7 vortec swap. It runs beautifully, really purrs like a new born kitten except the coolant isn't circulating. I put a new thermostat in and it still wont circulate and keeps overheating. But when I undo the top hose on the 5.7 radiator it does come out when the truck is running. Please help!