4EAT high speed lockup slip

I have noticed my 94 legacy transmission with 175K miles has slipped out of engagement a couple of times when cold at low speed and is running higher RPM than I am used to at high speed. 3500 rpm is 60+ mph. If I have the gear ratio figured out correctly, this should be around 2200 rpm in 4th (2.56 total reduction on a 24 inch wheel diameter). My initial thought was that it was not engaging in to 4th. I got the least expensive dealer diagnostic where they ran the car with a select monitor. They say it is getting into 4th but it is not locking in (therefore slipping I assume). They note a oil pump leak. They also say the lockup duty ratio is running 5% and that this is like having a front wheel drive. They conclude time for another or a rebuild tranny.

Any opinions on another course of action? I don't mind diddling around if it might get somewhere. This seems like it might be a pressure issue to the lockup clutch which may have a monitor point for checking. I have a steep gravel hill up to my house and I use the manual button for 50-50 power and have not noticed any problems here.

First post for me though I have received a good education form the dialog on a number of items.