Had the shift kit installed in the valve body the day before I left with my heaviest load yet. Tranny performed flawlessly. No hint of slippage and no clutch material or anything else in the pan. The new TC is still sitting in the garage, ready to be installed when I get time...
I'm heading out Wednesday with a lighter load. I've got three or four loads to go.
Apparently the shift kit improved line pressure enough to eliminate the slip. It feels better than my stock 38RE did in my 03.