91 Caravan Transmission shift problems

I have a 91 Caravan 2.5L non-turbo w/ AC, A670 trans. Every once in a while the transmission will go from 1st to 2nd and then straight to 4th (seems like fourth but I believe it's just a 3 speed with converter lockout. Feels like an overdrive gear or 4th I'm calling it). Then when slowing down to a stop sign or light it will stay in fourth and start shuddering when it gets to the point it should be in 2nd range. I manually shift it into 2nd and all is fine until I speed up again - straight to fourth. I have a small leak (another topic) and on occasion these problems seem to be because the level was a little low. Other times the level is perfect. I've recently changed the filter and fluid using +3. The people prior to me getting the van were using Dexron as they didn't know better and the dipstick even says to use Dexron II (not III). Any ideas? I've heard a lot about solenoids and more recently the grounding strap from the trans and maybe the solenoid pigtail conn.?

The leak seems to be coming from the right hand side (driver's perspective) output shaft. Or it maybe coming from up higher. What is the part directly above? Looks like a sensor of some sort and has metal flanged connector. It does not leak a drop while parked only when running/driving.

Thanks for any help,
Another Caravan owner with transmission problems...

When your van is cold, unplug the electrical connector right next to the transmission dipstick. You are removing voltage from the TCC solenoid. Drive it for a while. See what that does for ya.