I’ve got a 91 chev with a 700r4 that is driving me crazy, transmission worked fine then one morning I hopped in the truck and it goes from 1st 2nd barely slips in 3rd (free revs a bit) then immediately shifts back into 1st. I’ve checked the kick down cable and fluid. Fluid looks and smells brand new. 170k miles. I can get the truck well up to 80mph but no idea what my rpm’s are with no tach (probably pretty high but don’t sound high) HELP