Miss fire only when going uphill on highway

[Brayden1999]

2004 Tahoe 50k maybe on the motor less on the trans motor was put in in 2019 and trans in 2021. Runs great but the only problem is when I am crushing on the highway and start to go up hill maybe up a bridge or something along those lines it will start to flash the check engine light around half way up the climb. If I let off the gas for a second then get back into it it’s usually fine and goes back to normal. I am not sure what could be causing this I doubt it’s spark plugs, coils, or injectors because they are all around 50k with the new motor. But please let me know what y’all think and if I can provide any more info. Thanks!

[asilverblazer]

Confirm the codes causing the check engine light.

 

It could be anything - try to narrow it down to specific cylinder (codes). Then swap components from a known good (non-miss firing) cylinder to the bad one. Plug, coil, wire, injector, one at a time until the miss fire follows the last swapped item. That item would be the culprit.

[txab]

Check for intake leaks or exhaust manifold leaks. Check fuel pressure

[MORSNO]

Fuel pump going out could also cause this.  My last truck ('01 5.3) had the same issue when I was towing a heavy load on the highway and climbing hills.  The fuel pump was still operating but couldn't provide enough gas.

[asilverblazer]

Also, there is another thread on here with similar symptoms, seems that an lazy O2 sensor ended up fixing it. This was surprising to me, the only indication was the fuel trims on one of the cylinder banks was way off from the other. 

 

A scan tool that can show you cylinder miss fire counts, fuel trims and O2 sensor activity would be helpful.