I did some more tests & hopefully this will mean something to some of you out there that have more experiance with transmissions than me.

The squeak/squeal is the same in all gears/positions except park, it is still there in park but muck quieter. It's hard to describe but it sounds like a dry rubber squeal

I haven't taken it back out on the highway but it seems to drive foward fine although it does need more gas to go in reverse, almost like the brakes are on a bit.

I think I'll check some pressures & check back here before I take the pan off.