Have you done a THOROUGH check of the engine?
Mountains and altitude make a big difference--but--I wonder if the engine is running well enough to develop proper power.
Before I re-geared and hot-rodded, I'd be looking at exhaust back-pressure, fuel pressure under load, O2 sensor age, throttle opening when the pedal is on the carpet, and I'd verify the data stream for fuel trim, MAP and Knock sensor operation, misfire history, etc.
The engine is pretty well kept up. It had damn good compression, pretty consistent through all 8 cylindera. No misfire codes, and the ignition system was all recently replaced from coil through the new distributor (with a metal timing gear) to the spark plugs. Plus, I upgraded to the MPFI, so there shouldn't be a fuel injector issue there.
Fuel pump went out a year ago as well, so I bought a new Delphi fuel pump.
Since my cats had fallen off before I bought the truck, I had the rear O2 sensors deleted from BlackBear. I don't know the age of the upstream ones, so Ill definitely replace them now that you bring it up.
The biggest issue it had was a bad long term fuel trim on the passenger side, but there was a bad exhaust leak because of broken manifold bolt that caused a cracked manifold. I fixed that, so the LTFT is starting to fix itself.
The knock sensors were replaced a year ago. When I bought the truck, I found one sensor halfway broken so I just replaced them both.
I honestly haven't checked MAP and MAF sensor operation, but the truck currently doesn't throw any codes for anything related, so I never thought about it.
Good tips, though, thanks! Ill look into it more. I just kind of assumed it's in good condition. It idles really smooth, never hesitates, and adjusts to higher elevation really well. Hell, I think it handles long highway drives better than the '02 Impala I had did.
