No year posted is there a check engine light on and a wrench sign on the instrument panel? If so is this a drive by wire throttle body with a motor (electronic motor for gas pedal instead of manual throttle lever with a cable if so the motor went and your in fail safe/ limp mode go to autozone and have codes read for free then you'll know for sure what the problem is

Sounds like it goes into "limp mode" sometimes this happens to keep from damaging transmission. Transmission may be over heating or low on transmission fluid.