Simple. If it's a 3.3/3.8L, there was only one transmission made that will fit. The A604 is the monster you're looking at. But don't be confused. It's got a slightly different bell housing than those on the 3.0L equipped vehicles.
P.S. There were no Electronically controlled 3 speeds available for these vans.
The best way to tell is if it has "coil pack" on the front of the transmission with a large connector. If they are there, it's a 604. If they are missing, and all you see are a bunch of "adjustment knobs", then it's the non electronic 3 speed.