i would recomend a full trans flush at a reputable shop, not a quick lube cause the auto trans is a complax machine and will often malfunction if a little dirt gets in the fluid.

this is from acdelcotds.com
No Up Shift or No Down Shift from 3rd to 4th Gear or 4th to 3rd Gear

  • PNP Switch
  • Shift Solenoid No. 1 Circuit
  • Shift Solenoid No. 2 Circuit
  • TCM
  • Throttle Opening Signal
  • Valve Body
  • Transaxle Internal Parts