The AT in the F450/550 is the 4R100, virtually identical to that in the 250/350... Only difference is in electronics. The Cummins is not available in the Fords until you get to the F650/750 medium-duty trucks. Here's how it breaks down:
Cummins ISB (standard engine):
175, 190, 195 HP ratings
420-620 lb-ft TQ
(They are planning a 260/660 version for Dec. delivery)
PowerStroke (optional):
210 HP rating
520 lb-ft TQ
Caterpillar 3126B (optional):
190, 210, 230, 250 HP ratings
520-660 lb-ft TQ
Transmissions, 9 available:
--Two Eaton 5-speed manuals
--Two Eaton 6-speed manuals
--Two Spicer 7-speed manuals
--One Allison 4-speed automatic
--One Allison close-ratio 5-speed automatic
--One Allsion wide-ratio 6-speed automatic
***Also, new for 2001 is a 2-speed rear end.
Hope this answers your questions...