ES 300 Check engine :"OD-OFF"
 

My Lexus is in mint condition with 165K miles on it. Just replaced timing belt, water pump, cam seals etc. etc + front/rear struts and rotors. It needs nothing and love this 30+ year old car!!
Two moths ago the check engine light came on saying "OD Off". The code was PO753 - "Shift Solenoid Valve A (or valve #1) Electrical Malfunction". Every tranny place here in Eastern WA. declined to work on it. One very old established outfit told me "oh yes, it's those solenoids. Set up an appt. 3 weeks ahead and told me it will be $600 + parts. Two weeks later, I got a call cancelling the appt. saying they do not work on Lexus!! EVERY tranny outfit simply wanted to sell me a new transmission - essentially for TWICE (or better!) the hard, street, monetary value of my car!!
I have a decent garage with a hoist and decided to tackle it myself after watching a couple of YouTube very helpful videos. Ordered 2 rebuilt solenoids identical to mine from Ebay, checked them out that they work, bought a new wiring harness (from the top of the tranny to the solenoids) and installed them. After bringing the tranny oil level to specs, I took the car our for a test drive. I was singing Hallelujah for about 20 miles when all of a sudden, the check engine came back on and "OD-Off" blinking.
Here's what's interesting (1) with the OD button on the gear shifter OFF, if I turn it back ON while doing over 40, I can feel it going into overdrive and the RPM drops 250-300. Nothing changes on my dash lights.
(2) When on the freeway (with the OD button ON and dash "OD-Off" light blinking), doing over 50, I put the car into Neutral, turn off the engine, start it again, shift back into Drive and the tranny shifts into OD (saw this trick on YouTube). The OD-OFF light disappears for as long as I keep driving. The 'Check Engine' light, however, stays on.
The mechanic friend of mine who read the original code, checked it again and the same code P0753 showed up the same except it says "stored". He is at a loss as to what's going on. Can anyone help?

PS: I read earlier (separate) posts on this subject and one person said it was the Speed Sensor. Took out my Speed Sensor and it is in perfect like new condition.