i have a 94 grand cherokee with 134k miles on it, the transmission shifts fine from 1st to 2nd, but 2nd to 3rd it slips, if i let off the gas it'll shift in to gear but if i hit it again it slips, i've adjusted the tv cable, i took it to the dealer once and they said they adjusted the fluid pressure? it was fine for a couple months and now it's back, what could it be?