It seems you're talking about a different problem for each. Let's take the high gear problem first.

I would check the pressures at the 2-3 and 3-4 ports and see if they are within range. If not I would suspect a problem in the clutch packs as well as the main valve body. If they are but tend to "creep" into range, I'd drain the fluid, remove the filter and the valve body and check the pan for metal shavings. If you find none the clutches are probably still OK so remove the valves from the valve body and inspect carefully. My guess is that you've picked up some wear, but it may be confined to the o-rings. Clean the valves and the housing and if all spec out OK, change the o-rings and reassemble and recheck your pressures. Most times this will cure the high gear sticking problem.

The low gear problem on the other can be as simple as the cable adjustment or a defective vacuum modulator, or no vacuum supply from the cannister/booster unit. Check these first. If the problem still exists, again check your pressures. In this case I would be suspect of a bad sprag in the torque converter. Have it bench tested if you don't have the equipment to do it yourself. If it is a bad sprag unit, replace the entire torque converter and be sure to replace the front seal in the transmission itself while you have it down.

Spaw