Current OD reading is 308k miles.

So the past couple months I’ve had issues with vibrations at highway speeds. Now as of 2 weeks ago I couldn’t push over 75mph without a violent vibration. Checked the drive shaft and u-joints both are fine. Here about a week ago my harmonic balancer fell apart doing about 45mph and shredded my belt. Belt and harmonic balancer have both been replaced. Since then I’ve gotten a a Crankshaft position sensor code p0385 or circuit B. Along with 2 days ago after getting off the interstate I slowed down to 40mph and turned overdrive off. When I did it hard shifted and my O/D began to flash, from that point on I could do about 45-55 mph without pushing it to hard but I could feel the transmission slipping/ not shifting at all. I had my dad whos been a mechanic since the late 60s take a look and he said if you maintain throttle it eventually shifts.

When the O/D light flashes I can restart my van nd it’ll stop until it starts again which is at random I could have 5-15 minutes in O/D before it malfunctions again.

Checked differential fluid and refilled it.
changed crankshaft position sensor.
new harmonic balancer and belt.
We believe it may be an electrical issue considering it resets after restarting the engine. But I have talked to multiple people along with a scouring
forms. Any help will be greatly appreciated! I’m taking it to the shop next week but hoping maybe someone can help me out.