The transmission was rebuilt (according to the carfax) around 123k miles. I don't have any documentation, but the stall torque is around 2200 so I think there was some upgrading done? Anyways, the car now has 153k on it and there was some weeping from the transmission pan gasket so I replaced it along with the filter. It was driving fine for the first 500 miles or so after I did that, but I don't get on the highway much and my commute is just 5 miles across town. I took a longer drive and discovered that once the fluid got warm it would rev freely/slip and then slam into gear. On the way back it seems like the problem would pop up when I was pointed uphill so I thought it was a fill issue.

I took it to a local euro shop to have them do a drain and fill so that I could rule that problem out, but it didn't help. The thing that doesn't seem to line up with other things I've read is that I'm not getting any "slipping" while it's in gear, it's more like I'm getting a false neutral between gears. Going into 3rd gear from 4th gear (both under and not under load) is when the problem is really showing itself. If I shift up from 2nd to 3rd the car pulls fine and will continue pulling as it goes into 4th and 5th.

I'm not getting any codes, except for a 17115 that popped up as I was troubleshooting and the transmission went into 5th gear. After the transmission cooled it was fine and hasn't come up since.

So does this sound like something that removing and cleaning the valve body will fix, or am I in bigger trouble?