Aerovette

2015 GMC Sierra Denali 5.3l - As I get up on the highway at full throttle, the truck runs through all the gears and in 6th, around 4300rpm/83 mph, the truck stumbles and flattens out. On occasion it will max at 85 and regardless of throttle, will not go beyond 85. This happens about 1 day a week. Through the other gears, I think it passes through that rpm too quickly to notice a stumble. It occasionally stumbles at lower speeds too. Recent work done: New #7 lifter New injector at #7 Injector cleaning treatment at the same time as above New catalytic converters Oil change New Air filter Throttle body cleaned ONE time it threw a misfire code but I neglected to ask the tech which cylinder. I'm thinking new plugs, coils, wires, but I seriously don't think that is the issue. One day it runs like crap, next day like a scalded rabbit. No rhyme or reason to it.

2015 Sierra Denali 120006 miles. I bought this used and occasionally I would get a P0307 code. I'd erase it and it would drive for months with no issue. Last night I went to dinner..' all good. I start the truck to leave and as I pull out I get a stabilitrak light and a flashing CEL. Reduced power and bad idle. Today I: Disconnected the battery for a couple hours hoping for a miracle "reset" no luck. Swapped 1 and 7 coil, plug, and wire. No luck Observations: NO lifter tapping #7 plug was oily When no code is present, oil pressure is about 30. When stabilitrak light comes on, oil pressure increases to just over 40 and I can hear some sort of sound like air flowing or vacuum or something. When I clear the code, the sound goes away and the oil pressure goes back to 30. CEL comes on long after the Stabilitrak has been on a while. (minute or more) Only ONCE after I first swapped the plug, coil and wire, I got a cold rough idle code P050D V4/AFM does not engage