I have a 2006 AWD Suburban LTZ with 6.0, reman transmission approx 2 years old will hard shift 1st to 2nd only after being on interstate, after I turn off and it sets for 15-20 min it does fine, until interstate again then hard shifting 1st and 2nd starts again, anybody have this issue, if so whats the fix, thanks

 

try gmtnation
the site has good trans information.