1989 300SE Auto Transmission slips

I have recently purchased 1989 300SE 6Cyl auto non-turbo with 130 K miles. It slips when shifting up into next gear (all) on acceleration. Fluid is clear.

I can replace myself ( I think) with a salvaged one, rebuilt, or would like to try some things first.

Also, I assume this is 4 speed with lockup converter. How many RPMS should I turn at about 60. Does ~2800 sound right? Is Dextron the correct fluid.

Any suggestions appreciated.