resonator

Recently when I park the car on a 10-20 degree inclined driveway the car does not want to lock the wheels in park. Putting it back in drive and then back to Park usually works but you can feel the car "missing" the point where it would usually lock - a few ticks as it rolls. This is the 722.6 (if I have that number right) transmission.

I had the fluid changed by Dr. Bob (Springfield, IL) about 10k ago.

As a side note: it is generally icy weather out and I though initially it was just sliding but I have eliminated that possibility because it does not do it if I hit the e-brake. I once had this happen to a Jeep Grand Cherokee and it was actually an ice build-up but I'd hate to think those conditions would happen with this car.

Other information: Car has about 95,900 on it. Otherwise excellent shape.

What's going on with this thing? What ought I take a look at? Could it be as simple as the linkage bushings?

Thanks in advance- and Merry Christmas.