Stumble / miss at high rpm

[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.

[steelerdude15]

Did you clean your MAF sensor? If not, clean it and see if there is an improvement.