Neal,

I found this earlier when I was searching Dieselmanns technical bulletins

Reverse Engagement Stall:
Some trucks with the 4R100 transmission may stall upon shifting into reverse. This is usually caused by the torque converter clutch being engaged at idle. Engineering is investigating. Broadcast Message 1222.
If this condition occurs under cold temperatures only, it may be due to increased viscosity of the ATF. Ford is recommending changing the ATF to synthetic in this case. Broadcast Message 1435.

I know yours doesn't stall but it may just be a fluid thing.