Tranny slip in my 5.3 chevy Silverado 2004

Having a full and correct reading can be a problem, not servicing can too, wrong fluid, failed part causes wrong gear? does it have a code ?

No code. Tranny fluid could use a flush and be changed with new but it's not terrible. My truck was running right at 210 degrees where it always does so the truck was warm went into gear like normal just when I got on it getting onto the highway the tranny slipped

Nowadays when you tear em down, the frictions arent as substantial as they used to be. The ones i saw recent seemed kinda fragile. The best grip i ever achieved from a service was with "BG products" "ATC" trans additive we sold at the dealership. They have it at some napa's and some national auto parts where I live. My trans suffered from fluid level issues and tampering and that saved it for another year.

I'll give that a shot. Thank you very much