[99subhelp]

I have a 99 chevy sub with the 5.7 and I had the seal replaced under the intake manifold and now it miss fires when I climb a hill and get to peak it will missfire badly. It will never do it when your climbing the hill or on flat ground but only when the engine has been enganged on the hill and then comes off of a little. It only happens at speeds over 50 MPH. I have replaced the plugs, wires, cap & rotor, and the fuel filter. The dealer wants to replace all these parts again and charge me 500 for it. I need some Ideas. I took it to another mechanic and he sees it misfire with the scope while driving but can't pinpoint it.

Thanks

Tony