I've had the batteries both tested & they're apparently fine...I recently had the fuel module replaced & otherwise I've had it in 4wd low cuz its been parked in a snowy/icy vacant lot...

Any thoughts on why I would have a drain alluva sudden? Any known issues?

 

What has worked for me onother vehicles: Turn off all lights & accessories. Disconnect negative battery cable & hook ammeter between neg post & terminal. Ampmeter should show a draw if you have 1. If you have a drain, start pulling fuses until you isolate the circuit then disconnect individual loads until you find the problem. You NEED a wiring diagram. Since we have 2 batteries, I'd expect that the secondary be completely disconnected. Don'd ground the connections. On the last 2 where I suspected a drain, it turned out to be the battery. Batteries tested good, not great but were frequently leaving me in need of a jump. Google is your friend ie "parasitic drain". Problems are usually connection, switch or load.

 

im having a similar problem except my truck is 97 i'll go to get in my truck cab lights on, and as soon as i go to engage the starter,or even turn the headlights on and its drains my battery and i get nothing. then 2mins later the batterys have the juice and my truck starts up but then the gen light was on, i have no idea what this means. but my truck has done this to me 3 or 4 times. i checked all my fuses and there fine, i check the wire going to the starter that was nice and tight. gettin a little ticked off at my truck.

 

Well i would check your battery connections and wire connectors again and make sure they are tight. If you try to start your truck and the batteries are dead, they will NOT recharge themselves in 2 minutes and start the truck. I dout you have bad batteries.
My buddy has a 92 Dodge and that's exactly what happened to him. All of a sudden the truck wouldn't start, he'd only get a rapid clicking sound. The problem ended up being the starter wire had a bad/loose connection and was not able to draw enough amps to crank over. The way we determined this is I wiggled the wire while he attempted to start the truck. As soon as i moved the wire she started right up.
I hope this helps ya

 

i checked the connections on the batteries, not the starter yet. yah ur right if they were dead they wouldn't recharge in a few mins. but starter doesn't even turn over, but if i hit the brakes, or put any load on the batteries everything just goes out. i did get the clicking sound once. tonight trying to start my truck. i'll take a look at it tomorrow. it might be one of the wires needs replacing that would make sense.