Most likely something having to do with band B2. I noticed you replaced the B2 servo piston in an earlier post. Recheck the B2 servo if you haven't already. Unless the old B2 servo was in pieces or the lip seal had failed, I'd be checking to make sure the fluid level is OK, and if so, use a pressure gauge to check line pressure at the test port on the RH side of the transmission and see if that's OK (most likely is since reverse seems OK, but line pressure increases in R normally so it's wise to check line pressure in D) Either that or the O-ring in the B2 servo bore is leaking (the one that seals the B2 servo cover), but there'd be lots of fluid on the ground in that case. Another possibility, although less likely, is the selective pin that goes in the opposite side of band B2 fell out when you pulled the B2 servo. That can be reinstalled, but the valve body, separator plate, and B2 plastic guide have to come out, but that can be done from under the car in any case.

Without B2 (gears 1, 2, and 3) or K2 (in fourth gear) being applied, no torque can transmit through the rear gearset. However, with the wheels off the ground sometimes just enough torque can make it through the clutches and gearset to turn the wheels. Reverse works since the front gearset is outputting reverse to the rear gearset and there is a one-way clutch there that locks when reverse torque is applied, so no clutch or band needs to be applied in the rear gearset.

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Erich Loepke
2010 Ford Focus
Currently Benz-less