Trouble Code P0770 - Transmission Shift Solenoid E Malfunction

OK, looking for some experience or advice. On our 2001 Tundra 2wd SR5
V8 (66,000 miles) we had a couple of unexpected hard downshifts over
the last few weeks. Towed our trailer out to the desert last weekend
just fine (500 miles total with some 4,000 foot climbs) but after we
stopped about 25 miles short of home at a rest stop and restarted we
got a check engine light. Experienced a lot of slippage when we backed
the trailer into the driveway. Trouble code is a P0770 which reads as
a Shift Solenoid E Malfunction (Shift Solenoid Valve SL). Explanation
is that the Shift solenoid is stuck open or closed, valve body is
blocked up or stuck or there is a problem with the lock-up clutch.

Dropped the pan, pulled the solenoid and it appears to test fine (power
on = valve closed, power off = valve open). Appeared to be a minimal
amount of fine metal stuck to the magnets, fluid was clean and
smelled fine. Looks like the next recommended step is pulling the
valve body to check it out but I'm not crazy about spending that much
time on it at this time of the year. Of course I fear the $$$ for a
dealer repair.

Anyone have a similar experience, outcome to share or recommendations?

Thanks, Gary