I recently replaced the intake manifold gasket on my tahoe (5.7 vortec). After reassembly the engine has a miss when at cruising speed while trying to maintain a constant speed. Codes are #4 cylinder misfire and all banks rich. Replaced plugs, wires, cap, rotor, #4 cyl injector (individually, not whole spider assembly). Also ran two cans of techron additive through it. No improvement. Tired of throwing money at it. Any help would be greatly appreciated.