1994 Honda Accord A/T Gear problem

My car suddenly jerks out of gear, its an auto tranmission.
It revs as high as "2800 rpm" before changing from 1st to 2nd gear, it revs up to 4000rpm before changing to 4th gear or never changes at all till I release my foot from the pedal up to 2000 rpm. I've chaned the gear oil several times, even had to replace the whole gear. After replacing the gear, it ran smooth for 2weeks and its bak on the same fault. I need help solving this please.