Suggestion: try testing in reverse gear if you get the same slipping problem or not. Could be loss of pressure from the pressure pump of the tranny... Kung Ok sa atras, forward clutch problem probable. Then again, kahit anong problema, kung di nakuha sa tranny oil change and clean-out, baba tranny pa rin ang bagsak!

If you do find a good tranny mechanic, please let all know!