Thall

Alright I have a 2015 Chevrolet Silverado 1500 it has the 6.2 in it with the 8 speed transmission. I’v had some codes pop up off and on for the last 4 years that nobody can seem to help with or take the time to diagnose. I’ve been told new motor and new transmission. Ive got a random or multiple misfire. A misfire on cylinder 8. A cold start rough idle, which is the most frequent. A transmission fluid temp sensor. A transmission control system sensor. A mechanic told me to buy a scanner and delete the codes. It drives pretty smooth but uses more fuel and feels like a dog. I’ve changed plugs/wires/coil packs. This has been like this for 4+ years and smooths out every time I delete the codes. What’s going on ? Shifts like butter. 73k miles

So I’ve got a 2015 1500 Silverado 6.2 with the 8 speed. She now has 72k miles and I’ve been dealing with the same codes along with random misfires cold start rough idles. Replaced the plugs wires and coil packs no change. Local transmission shops have all quoted me around 10k for new trans and install, not gonna do that so what are my other options ? And how would that fix my misfires ? Also has a slight shake or shudder on the highway. When I delete the codes she runs and shifts smoothly just with a loss of power. Nobody can seem to figure it out