I am hoping someone here can help me AND my mechanic with a strange problem I've been having with my van for several years. The reason for "several years" is that I CANNOT *MAKE* it happen...it just happens when it feels like it!

Here's how it usually plays out:
I'm driving with cruise control on (doesn't have to be on, but often is)
The cruise control cuts out
The overdrive light on the shifter starts blinking (not always, but usually)
The transmission has great difficulty shifting up or down...it makes a roaring sound, then BANGS into gear. Sometimes it feels like it's slipping gears. This happens both when speeding up and slowing down
If I keep driving - carefully - it goes away, and when it does the overdrive light goes out (if it was blinking) and the cruise control comes back and can be set again

When it happens and I'm not actually using the cruise control, I can't use it until it all clears up at the same time.

I just had a new transmission put in the van (burned up my previous one on a mountain), but the problem still occurs. My mechanic did find a speed sensor that was not registering properly and replaced it. He also found that the (darn can't remember the exact name) - but a sensor that tells the transmission where to shift was off by 1 tooth.

The last time I brought the van home, when they thought they had found the problem, I drove it from North Georgia to South Carolina (about 100 miles), using cruise control almost the whole way, with no problems at all. Then I drove it on short trips all the next day with no problems. Then I drove it to work (about 30 miles) with no problem. But when I left work, I didn't even get out of the parking lot and the transmission started shifting rough and the overdrive light came on. When I got to the highway, the cruise control would not work.

So I drove to my mechanic's shop (about 30 miles) and the problem was so bad I was afraid I wouldn't even get there...but about 10 miles away, it all went away. I've NEVER been able to get it to happen for my mechanic!

It doesn't seem to matter if the transmission and/or engine is hot or cold. I once drove it from Georgia to Massachusetts with no trouble at all, but on the trip home the cruise control cut out in Virginia, the overdrive light started blinking, and the transmission shifted rough. Then, about an hour later, it all cleared up and I drove all the way to Georgia with no problems.

On the other hand, I've had it start before I even got out of my driveway, which is VERY short!

I'm sure stumped (don't know much about automatic transmissions anyway) and my mechanic is stumped too. Whatever it is I don't see how it can be the transmission itself, since the problem is still there after installing a new transmission. I'm thinking it's got to be some kind of controller...but what controller I have no idea.

ANY suggestions?