A833 getting stuck in 3rd gear

Any one ever had a problem with a A833 OD getting stuck in 3rd gear? This happen right after I bought the car, I thought it was stuck in 4th (want come out of 4th). I pulled the side cover and it was actually stuck in 3rd, 3rd was pulled back past the ‘’dogs’’, it clicked right back in once I pushed them down. I thought it was because the old shifter did not have stops and I just pushed 3rd to far. Spent $700 on a complete new shifter with stops and adjusted it for hours until I could slam it through the gears and it was fine. Just took a easy drive to the gas station, shifted like a champ all the way there and the dang thing is stuck again. Trans was rebuilt right before I got it. Also does anyone make a plug for the rear shaft so the oil stays in when you pull it? I bought one on line but it’s worthless. This is my first Mopar and it’s about to drive me nuts!