Transmission completely lost power?

[spaceghost]

Had to have my '93 EV GL (auto trans) towed today after I lost power... Was driving just fine all weekend, then today after being stopped at a red light, stepped on the gas and the engine just revved, like it was in neutral--no power going to transmission. Pulled over (luckily I was on a slight downhill so this was possible), checked that it was indeed in drive, tried manually downshifting, tried reverse, tried turning the van off and then back on, and nothing worked. Checked ATF with the dipstick and it seemed fine too (although it was warm when I did, so I'm not sure how that affects readings).

After the tow truck dropped it in my mechanic's lot to look at tomorrow morning, I tried it one more time, and it worked again (drive and reverse both had power). Anyone recognize these symptoms as being indicative of anything specific? The fact that it never went into limp mode before going out (and happened so out of the blue) and the fact that it "fixed" itself after the tow truck ride seem odd to me. The previous owner had the transmission rebuilt just before I bought it, less than 3k miles ago.