I've been getting a misfire on cylinder 4 for quite awhile now. It only happens under load. Before I'd really have to push it before it misses, but now it'll miss any time I'm over like 70mph or have to punch it getting on the freeway. I've changed the plugs, wires, caps, rotors, and fuel filter. I've also notice that while its missing and afterward there is a smell of exhaust in the cab. I dont think I have an exhaust leak or anything, cant hear one at least. This thing is really pissing me off. Any ideas? I drive a 99 4x4 tahoe with the 5.7 vortec.