You may want to test governor and modulator pressure for your specific transmission part number. There is an ASTG manual floating around on the Internet that has all the testing procedures and values for the various different transmission part numbers.

How many miles on this car? If a high mileage example, you might try a bottle of the yellow Trans-X. If you have a bunch of varnish or sludge built up in the valve body it could possibly help. My SDL sat for a decade with old fluid in it. Transmission was absurdly rough when I put it back on the road, felt like it had a drag shift kit in it. Every shift was delayed and violent. Yellow bottle Trans-X helped a surprising amount. I'm not a believer in "mechanic in a bottle", but sometimes it's a band-aid that actually works.