ok my 1997 ranger 2wd 3.0, has 93k on it, when i first got it had 72k, noticed it shifted hard from 1st to second, and occasionaly hard downshifting from 2nd to 1st this happens when you drive the truck around for about 5 minutes. when this happens, if i turn the truck off and back on again it shifts perfect, then about 5 mins later it starts to act up again. i changed the trans fluid twice and filter. and also the speed sensor.

this truck i use for my business so any advice will be appreciated. thanks!!!!