Transmission problem no 3 or 4 gear engagement

[crhenkel]

So I have a 1986 w201 190E 2.3-16v with an auto 4 speed 722.410 factory tranny and about 105k on the car. It is in great shape and really no issues with her except the tranny problem now. It was sliding from 2 to 3 sort of slow and sluggish so I thought what better time to change the over due tranny filter and fluid and leaking tranny pan gasket. Thought it might fix the 2 to 3 slide issue if I put new filter and fluid. I used a dexron II / III trans fluid as the new fluid and I put some anti slip additive in it too. This was all after I put some flush in the trannny and drove it about 5 minutes and dumped the old fluid and flush additive. I refilled with a Dexron II / III trans fluid. It drove much much better, the slip from 2 to 3 was all but gone. THEN, two days later after maybe 20 miles max, I drove my girls to a friends house and on the way the tranny seems to have forgotten third and fourth gear even exist. It just happens in an instant while driving about 35 mph in town. Gone. So now I am hoping it is a piece of trash that broke free from the work I did. I just need to get the 3 and 4 gears working a gain. Tons of revving up but no grabbing in 3 of 4. 1st 2nd and reverse are all fine. I am hoping some crud just got busted loose while working on it. I may try to flush it all again and see if I can get what ever might be stopping the 3 and 4 gears from working and get them going again then it would all be good.
If I have to , should I buy a rebuilt from the build shop in California? The tranny and torque converter are all rebuild all ready, I just have to reinstall and adjust ( cost for rebuilt is about $2000) or do I even think about pulling the tranny apart my self, I have several manuals but no transmission internal work experience.