Freewheeling in "D" or "R" at idle

[dcarrb]

I have to hold the brake when transitioning from one direction to another, or from a stop, on an incline, as the car will roll at idle, forward or backward, as if the gear selector were in neutral. Raise the revs a bit and it'll grab and go.

ATF is clean, clear, and full. No measurable drop in fuel economy (this has been going on for awhile). No unusual delay after shifting from R to D or vice-versa. Good bite in all gears, at any speed. I drove the car 150+ miles Friday, fairly hard, Interstate to curvy, hilly 2-lanes, and the tranny performed flawlessly in every other respect, near as I could tell. I've put over 50,000 miles on this car and believe I'd notice any change in behavior.

So this seems a minor issue, but I'd appreciate some opinions as to what's up, and more importantly, if this a foretaste of bad things soon to come. Could it be something as simple as a bad signal from the TPS?

Thanks,
dcb