[77newell]

This is simply a SWAG. Since it all seems to work fine with the cruise control on but not with the normal foot throttle maybe the TPS (throttle position sensor) or circuit has gone whacky. I haven't a clue how to test this except to alternately use the throttle and the cruise to run the engine RPM up and down. If cruise works and the throttle produces odd changes you have your culprit.

Good luck