(Automatic tranny, 187K mi)
Pressing pedal to the floor (at any speed from idle to midrange) causes car to slow down! (From idle, it will accelerate for a split second, then slow, then accelerate, then slow ... all the while with the pedal to the floor.) If I back off the pedal a bit the car will accelerate moderately, as it should. Usually.
Any attempt to pass on the highway becomes an embarrassing no-go. "Harry, why does that car behind us keep pulling out to pass only to pull in behind again?"
Even accelerating up a moderate hill at highway speed will usually result in the car stumbling, bogging down until I ease off on the throttle. On my last trip out of town I could drive a maximum of only 60mph. When I tried for more: stumble, bog, slow-down ... and very foul-smelling exhaust.
FWIW, symptoms seem to occur only after an extended drive.
TIA, Puzzled in the slow lane.