4L80e 1-2 shift issue
I have a 04 gmc sierra 2500 4wd with a 4L80e. When I take off from a stop it shifts hard from 1-2 if I accelerate too quickly. After that everything shifts fine. Now if I start off with the tow button engaged there’s no harsh shift at all. To me it sounds like it maybe a pressure issue, but I’m no expert on transmissions. Fluid looks fine, it has not overheated, I don’t see any transmission codes on innova 7111 scanner. I’m going to do a fluid and filter change. While I have the pan off is there anything I should test or look at? Are there any common fail points or replacement parts to have issues? Transmission has about 90k miles on it. I would rather try a few hundred dollars in parts instead few thousand on a transmission. Appreciate any advice.