2001 gmc 2500 6.0 random hard shift due to tuner

[Ironbull2500]

I recently bought my 01 2500 6.0l and it was tuned to add some power by the previous owner to the guy I got it from. The guy I bought it from said sometimes it'll give it a hard shift he thought it could be fixed if the pressure sensor in the tranny was removed or just replace the pcm. I want to know what you guys think I should do. It rarely ever happens city driving but I do alot of highway commuting to school and it's more frequent on the highway. There doesn't seem to be a pattern to it I just don't like that it shifts like that it can't be good. I feel like the best way to fix this is to just get a new pcm. Any advice would be appreciated. It's lifted 6in on 35s if that helps