2003 Denali Runs Rough at 55 mph and 1500 RPM

[burkbunch]

I have an '03 Denali with 66K and when I drive on the highway and pull a slight incline at 55 mph and 1500 rpm the engine runs rough while in overdrive. This goes away when out of overdrive and up the rpm's and does not do this at any other speed or rpm. I can watch the rpm guage and it will fluxuate and I can feel like a miss in the engine. Again this only happens at around 55 mph at 1500 rpm when pulling a slight incline in overdrive.

This vehicle has the 6 liter and runs great at all other times.

Any ideas? Still has the original plugs and wires....

[maxwedge]

Typical misfire symptoms usually caused by plugs, wires or a dirty/bad injector.

[intrcptrbird]

Yeah I say plugs and wires. I had a similar problem and turned out that my POS Bosch plugs I just bought had gone bad. Replaced them and the problem went away.