'17 LS struggling on mountain roads

[GranPrix]

107k OEM plugs and wires. MAF was cleaned about a year ago and was checked before the trip. Coils are still originals. Had to hold off on those… $$$ Original cats… I should get new cat sensors now that you mention it. MPGs haven’t changed, getting an avg of 18

 

[BlaineBug]

Clean the MAF sensor with appropriate MAF sensor cleaner for starters.

Nevermind, saw your page 2 reply.

 

[BlaineBug]

107k OEM plugs and wires. MAF was cleaned about a year ago and was checked before the trip. Coils are still originals. Had to hold off on those… $$$ Original cats… I should get new cat sensors now that you mention it. MPGs haven’t changed, getting an avg of 18

Was it legitimate mass airflow sensor cleaner? Brake cleaner can cause issues. CRC MAF sensor cleaner leaves NO residues on the sensor wires unlike other solvents.

 

[Doubeleive]

I hate to say it but if the engine is running good then you have to start poking an eyeball at the transmission
but you shouldn't have a misfire, how did that occur? check engine light?

 

[GranPrix]

Was it legitimate mass airflow sensor cleaner? Brake cleaner can cause issues. CRC MAF sensor cleaner leaves NO residues on the sensor wires unlike other solvents.

Yea legit MAF cleaner

 

[GranPrix]

I hate to say it but if the engine is running good then you have to start poking an eyeball at the transmission
but you shouldn't have a misfire, how did that occur? check engine light?

I thought about that.

The check engine light came on briefly. I was driving in automatic and switched it to manual so I could downshift it myself. When I did that it for some reason it threw it into 4th gear and rpms shot up to 4k and I up shifted to 5th immediately and everything went back to normal. Check engine flashed for like 3 sec.

 

[Doubeleive]

any history codes saved? if the cel came on and you haven't disconnected the battery since then, then there should be a historical code saved

 

[GranPrix]

any history codes saved? if the cel came on and you haven't disconnected the battery since then, then there should be a historical code saved

P0113
P0300
P2227
P2228

 

[Doubeleive]

P0113
P0300
P2227
P2228

aside from the random misfire those all appear to me to be intake related problems, which I bet could be causing the misfire.
I am no expert but if it were me I would maybe check for a intake leak by spraying some starting fluid around the edges of the intake and see if the idle changes and inspect the whole intake and make sure everything is on nice and tight, nothing incorrectly installed, cracked or broken, if nothing happens then aside from paying for a shop to check it I might just replace the maf sensor and map sensor and possibly even the throttle body, yes that's a shotgun approach and not the right way but if there is no unmetered air getting in then it has to be something
@swathdiver may have a more diagnostic approach, but you need a tool like a tech2 to help

 

[houstontaylor]

My 2003 Tahoe has no problem with the mountains of Colorado. I did replace the engine at 290,000 miles (now has 331,000 miles) due to sudden increase in oil use and that did help with hills and acceleration but it wasn't bad before that either.