W124 300TE Does Not Upshift

[Dave804]

Hey Guys,
I hate to be the noob and start off with asking questions. But, I've got limited tinkering time because of work and want to make sure I'm looking at the right places for my issue. Car is an 8/88 300te automatic. Mileage reads 208k on a dead odo. Based on service it has about 212k. Car runs well, got it for $1300 and am loving it so far.

The neutral safety switch is out. The coolant gauge occasionally decides not work and there is a surge at idle. I believe they are all related an am waiting on a new OVP to come in Monday. The idle surge is between 1-2k when the car is first started and coming to a stop. Regular idle is about 500.

The transmission will not upshift under regular acceleration. Driving on the highway it continues to rise in speed until engine speed is about 5k. A quick blip of the throttle causes it to upshift so that engine speeds are normal (say 3500 and below). Then after a time it continues to rise until you have to repeat the process. Once, only once it has slipped into neutral. What I believe to be neutral. I was going 70 and coasted off the gas for a prius. When I got back on the throttle it revved freely and went nowhere. Once again with a clip it went to the correct gear. I have no delay in engagement with the selector, no hard shifts, noise, smells, etc. The fluid level was not at max but very close and had no burnt smell.

I believe (in order) these are the best to check?
-Plastic linkage bushings
-Kickdown switch
-TV cable
-Fluid and filter flush
-Fried tranny? Haha.

I appreciate the help guys. Y'all come highly recommend. Its Dave in Richmond, Virginia by the way.