[ImperialCrown]

Usually bands loosen gradually due to wear. I have never seen one self-tighten.
How is Reverse? You have a properly adjusted manual throttle kickdown linkage, correct?
I would do a seal integrity test with a rubber-tipped air gun. You want a 'thump', not a 'hiss'.

There is really no spec for these adjustments & under most conditions, they should be left alone.

 

[ImperialCrown]

Probably not a band adjustment issue. Pressure readings are good diagnostics. Low pressures are probably from worn, leaky seals.

 

[ImperialCrown]

Air pressure tests are useful for a quick actuation test & apply/release comparison of the clutches & bands.
An aftermarket valve body can make pressure checks difficult as they might vary from what the factory service manual calls for.
Things like clutch pack clearances & lip seal condition (hardened rubber from heat, etc.) are best done visually & with the transmission disassembled.
If the band adjustment can't fix the symptom, the clutch has to be suspected.