Transmission shifts from OD to 3rd when I let off the gas...
2001 Ford 5.4L w/ 4R70w, 66k miles
Just as the title says, when driving at highway speeds, when I let off of the gas, and the trans will downshift to 3rd then shift back up to 4th. While cruising around 45mph, with the gas pedal between 0%-5% open, it just jumps between 3rd and OD. If I give it say 50%-75% throttle, and accelerate to 80-85 mph, all of the upshifts are perfect, in fact if I am crusing in 4th, then give it 75% throttle to pass, the 4-3 downshift is perfect.
That leads me to believe it's a vacuum or electrical problem, maybe a sensor or controller issue, but not a mechanical failure... but then again, I don't have much experience with these.
Any help is appreciated!!