A advanced scanner can monitor a number of key sensor inputs and may provide a clue; Long Term Fuel Trim (LTFT), STFT, Manifold Air Pressure, etc.
If fuel supply is cause of loss of rpms, power then LTFT and STFT should be indicating lean conditions.

Does check engine light work (comes on when keyswitch first turned to On)?

good luck

 

Yep check engine light works.
Just drove it. It really acted up this trip. Drove maybe 5-7 miles Still no codes lit. Quit acting up jst as i got home, I have been sitting here in driveway with car varying RPms from 1000 -1500 for,quite a while , issue has not come back. Maybe it is more of an engine load when warm?

 

Just drove it again approx three miles. No issues. Maddening....