42RH advice needed

Headintheclouds said
Most of the fluid was drained for shipping before i got it but it didn't look too bad. It has new fluid in it now.
What is most likely to be worn out?

If the trans did what you described with the new fluid it would smell like a forest fire.
Drop the pan and post a couple of pics.
That will tell a lot.

Sounds like a burnt forward clutch to me, and possibly the front band.