Was driving my '92 freeway speeds and without a noise my automatic transmission slipped into neutral. I pulled off the road shut it off. Restarted and it shifted into gear but would not shift into second. Going uphill pulling into a parking lot i lost power again and could not shift into any gear including reverse. Shutting off the car for 5 minutes and restarting it shifted fine. Checked the fluid level and it'* fine. Flushed the transmission fluid 7 months ago and haven't had a problem until now. I'm taking it to a mechanic, but I'm just wondering if there is something obvious i've missed. I know there are several other posts with similar problems, but I didn't see any answers.

Did you check your level when hot? When it slips from gear check the fluid, is it foamy or clear?

Yes it was hot and it was clear and red, not foamy.

How many miles is on the trans? There is a chance the filter is plugging up, even though you did a flush. I personally do not recommend a flush on a older trans. doing that can knock things loose and cause more problems. A simple fluid and filter change is fine. If the fluid is dark then doing that again 6 months later is all that is needed.