transmission slips when shifting into 4th gear.
If you let off the accel then it will shift into 4th. can I do anything to fix other than total
Besides locking out 4th, which I'm unsure you can do on your Saab, The overdrive band is probably burnt or worn, so you will need to replace that, and you probably already know that when you go into the trans you might as well rebuild. See if you can find a used trans at a auto recycler, might be a little cheaper. On a side note, does it happen on other gears, the reason I ask is maybe your motor mounts or trans mount is worn or broken, changing the driveline angle.
best you can do is change fluid and filter in trans. control pressure is lagging ,investigate if Saab has adjustable kick down control pressure as most older cars used to have