Sorry about a late reply. Dealing with an ice storm and NO electricity kinda puts the stops on any computer type work. Been "isolated" since Wednesday except for a brief moment on Thursday.

Slips huh!? When? 1st through 4 or in OD? Different devices transmit power during those two states.

1 through 4 slipping is Sprague clutch or your engine clutch IF there is no internal hangups of the hydraulic controls for the OD. Slipping in OD can have as many as 8 different or combined causes.

Power handling of the D type. In 1 through 4 with a properly functioning Sprauge clutch and OD control system....you are limited by the adaptor to the transmission. You will sheer that before anything internal to the OD. Somebody out there has a 544 set up as a dragster and has asked me for the adaptor to the trans or if something stronger is available. His has a crack in it. Couldn't help him except to suggest to make a stronger adaptor.

In OD. With sufficient hydraulic pressure, the adaptor again would be the limiting factor in the D type. The J type would tend to strip out the sun gear on the inside of the cone clutch if the adaptor held. How much power that is I have no idea since it also depends on how heavy the vehicle is. At start from stop, there is a greater force moment than when rolling.

Duane