2001 dodge ram 1500, 5.9 4wd...wont go pass 12mph and seems like it wont shift. does make a whining noise but no grinding. chngd out the output sensor and neutral safety switch but nada....chkd the existing fluid and no shavings or nothing out of ordinary. Sometimes when it sits it will go into gear and shift but after a few minutes right back to square 1......need help TIA