Transmission delay to not engaging

[SLRohan]

06 EB

The transmission is not engaging in drive, second, or first. Goes into reverse and neutral fine. Once it runs for 15 mins and some revving it will engage into 2nd and then I can put it into drive and it runs fine until put back into park

Codes read for a p0720. Replaced the output speed sensor. Completed fluid change and filter change.

Still nothing. Out of ideas. Anyone got anything?

 

[SafariGoneWrong]

I’ve had the C6 in my Bronco apart twice in the last 15 years but never a 4R70/75. But there are similarities. I’d bet the forward clutch is shot, whether that be the piston inner and outer seals or the sealing rings on the stator support. Anyone with 4R70 series first hand experience?