There are only two external adjustments for the 722.3/4 series transmissions.
1) Bowden Cable.
This cable connects up to the throttle linkage and generally affects how long the transmission will hold out gears. Roughly,it controls where the shift point occurs.
2) Vacuum Modulator
This device controls how much vaccum the transmission uses when it softens a shift. More vacuum = more clutching = more softer shift. If this is adjusted for too much vacuum flaring/slipping can result.
After you've checked the fluid level and confirmed that it is at the correct level and not burnt, I would recommend that you disconnect the vacuum line to the transmission and see how it drives. If the problems persist then you can rule out a vacuum problem. Pretty easy to do.
Some other common problems
-B2 Piston Failure (Not super common in the 722.4 more so in the 722.3)
The (infamous) B2 Piston
-Governor Gear Failure (Unique to 722.4 I believe. Plastic gear breaks and you lose upshift ability
If you do some googling you should be able to source yourself the "ATSG 722.3" which is a service manual with a troubleshooting section that might help further.