[Maleficio]

If you had a vacuum problem, you'd feel hard, abrupt shifting, not really loss of performance, .......save for the effect a vacuum leak has on air/fuel control.

Before you do anything else, I'd replace the fluid yet again with a quality synthetic, like from Amsoil.

I'm running Castrol ATF, and I don't like it. Also, I had no good way to flush out the old fluid from the cooler and lines, so I have a mix of old with new/cheap fluid. But I did drain the torque converter.