Reman 5R55S Throwing P0741 (Flashing O/D Light)

[metrolink]

I had a reman 5R55S installed at the end of July, filled with Mercon V synthetic. Drove fine for ~6 weeks, then the O/D light started flashing with P0741 (Torque Converter Clutch Performance/Stuck Off). No other codes.

What I know:

• Fluid may not have been set correctly at install (engine running/warm/check plug). Possibly overfilled. Tried to check the level with a T27 bit but the drain plug was a T30 and I stripped it . (New plug coming in this weekend).
• Cooler/lines were not flushed or replaced (lesson learned).
• No external leaks.
• Using OBDLink MX+, I logged the TCC data:
  • TCC Solenoid % = 100%
  • Slip Actual = ~200 RPM
  • Slip Desired = ~1020 RPM
  • Engine RPM ~1770
  • Trans Temp ~117°F

Symptoms:

• PCM is commanding lockup, but clutch won't fully apply.
• Solenoid seems to be working electrically (otherwise I'd see P0743 too?).
• Code is consistent after driving at 45-60 MPH.
• Car drives fine otherwise, no noticeable slipping in gears, just the code.

Before I drop the pan this weekend (replacing stripped drain plug, planning fluid/filter, cooler line flush etc.), is there anything else I should be looking for outside the transmission?

Note: It's a Street Smart reman with warranty, but I'd like to rule out anything simple before I go through the claim process.