1999 Dodge Caravan Erratic shifting

3.0L V6. Issue/ question is as follows. Driving and depending on load (hill) or on highway the trans will shift up/down between gears and not hold them as used to. Example is highway driving about 60 will feel/hear shifts between 3rd and OD continual. Will not hold OD during level highway area but will downshift with slightest change in pedal or incline. No engine codes. Engine vacuum steady. Not stalling out. Speedo stays accurate to speed going. Trans fluid good, not burnt. Hot or cold engine or trans. No harsh shifts. I see notes about shift solonoids for issues with not changing gears but the trans does change but not hold gear as used to. Batt reset, trans reset (ign on/off 4 times?) Thoughts on isolation or prior?