Well guys, the van is FIXED! Halejuljah!
I spent most of Sunday with a guy in my area who has a few of these Astro's in his yard. What really set me off in finding the true problem was listening to what a real Astro is supposed to sound like, in many different states. Most particurly, in diagnotic mode (when you connect ALDL terminals A + B). Since I bought it, it had made this funky sparking sound, coming somewhere from the TBI unit, but I coudn't pinpoint it. I assumed that it was a natural sound during diagnostic mode. But then I noticed that after the van stalled, and I left it with ignition still on, I could hear this muffled sparking sound. It sounded irratic and random, sometimes going for 20 seconds before it'd sound again. Guess what it was. The sparking noise was coming from the injector electrical plugs! So at first we thought, why not swap in a whole TBI unit since we got one sitting here. Van ran better, but the "sparking" sound soon reoccured after a short test drive, then it stalled. So really there wasn't any other choice - it had to be the ECM brain. And so we threw in the closest model we had sitting around. Same service number, from the same type of engine. VOILA! Holy crap we did it! Have driven it all day and night since, and its running fantastic.
I'm telling you guys, if any of your vans are giving multiple trouble codes, suspect the computer. And if you can try another used ECM in yours as a test, I'd highly recommend it. These computers, honestly are far too finicky. The trouble code 42 had nothing to do with the actual problem. I may or may not go get my computer reprogrammed. It should be worth it, for $100 or so, to have a spare working ECM around...
By the way, thank you all for your help and advice. I know you all have lives and busy ones at that. I'll be sticking around this forum... its a very helpful site.