I have a 99 suburban, 5.7 vortec. Idles great. Once it warms up it still idles great but it spits, sputters and dies while trying to drive. It backfires and barely stays running. Shut it down, let it cool off and its fine again until the temp comes up to operating temp. It has had a new distributor, plugs and wires, ignition module, coil, crank sensor and coolant sensor all replaced with no fix. I do however have a pretty good exhast leak at the manifold donut on the passenger side. I dont know if thats an issue causing these problems. I am planning on fixing that tonight. Any input on why this motor acts up at operating temp?