I have a 2001 I 30t. Bought it at 60,000 real miles, several years ago. At that time had the transmission flushed at a shop that used one of those pumps.

I was driving the other day, about 50mph. All of a sudden it felt like I was in Neutral. Motor running fine but no power to the wheels.
Coasted to a stop. Checked trans fluid it was fine.
Put in in R and to my surprise, it backed up.
Put it in D and to my surprise, it rolled down the road. First gear, fine, second gear, fine, then at 35 mph it shifted into the Twilight Zone.
Motor fine but no power to the wheels.

Coasted to a stop again, it would not downshift while rolling.
Put it in P, put it back in D, same thing. First and second fine, but apparent neutral for third gear.

I did this 3 times, had to go 3 miles, put the flashers on and put it in 2 and drove there at 30mph.

Had it towed to the transmission shop, they drove it the next day for 10 minutes and it worked fine! They sorta thought I was making it up.
I told them to drive it for 25 minutes and get that transmission warmed up.
They did, and it worked fine again.

What is wrong with my car?

 

I realize this is an old post, but I found it searching for something else.

My guess is that when the transmission was flushed, it dislodged some gunk and that clogged up a valve body somewhere in the 2-3 shift circuit.

Based on what I see here, I might be inclined to put it on the road for a few hours, get the fluid circulating at temp and hope the filter/screen catches whatever it is. Another option might be to flush again and get the floating gunk out.

Or, since all is well... leave it alone and drive?