1999 w210 722.6 not shifting into top gear
 

car is a 1999 w210 e300 turbodiesel om606/722.6 with 248,000 miles

recently purchased from 2nd owner of 10 years, but no history provided (long story) engine runs great but initially the transmission was going into limp model, stuck completely in 2nd gear. It all started after I first tried shifting into a lower gear than "D" and immediately the Check Engine light came on.
New battery- no improvement. I cleared the codes with an MB STAR equivalent and replaced the transmission conductor plate, electrical conductor, filter (and fluid drained)

it stopped setting the speed sensor codes (from bad conductor plate) and hasn't gotten stuck in 2nd gear since, so that made a big improvement, but it's still not shifting into 5th gear and isn't locked up on the highway. I've got to fix it before I can start regular highway driving. (2800rpm at 65mph just isn't cutting it on a diesel) but I'd like to get input from you guys in hopes to avoid throwing more parts to it than needed. I've done countless searches on multiple forums and haven't found much info on the causes of this specific issue. All seem to focus on the conductor plate, which I did need.

There definitely seems to be something up with the floor shifter. There are a lot of posts about a drink spill causing a limp mode condition (but not of just losing 5th gear) Instead of taking a wild guess and replacing the $500 shifter assembly I pulled it apart and there was light oxidation on a few electrical contacts so something likely spilled on it at some point. I cleaned everything and the PRND4321 indicators started working (except for D) and I'll probably be buying a new one soon, but have doubts that's the only culprit.

Other things I am thinking of replacing-

valve body springs and sleeves
solenoids in valve body (no codes had set indicating it)
TCM (i pulled it out and checked the board for anything obvious but that didn't show much)

any input appreciated