94 G30 Rough idle & stalling when stopping

Bought a 94 G30 Sportvan at the local State auto auction. Had blown engine, 350 5.7 TB. Replaced with rebuilt long block. Engine starts and runs fine, but when shifting into gear and almost at every stop the engine will stall. Will fire right back up and run down the road just fine, but the stalling is becoming a major pain, esp. whening slowing to turn into a driveway or stopping at a stop sign. Using the existing gas that was in the tank when purchased. Rough idle too, surges up in RPM every 15-20 secs when just running in place. Based on paperwork, figure the gas in it is at least a year old. Van does not get much use, as in 60~ miles in the past 2 months. Any ideas?

Any check engine lights or code?

Check EGR valve for sticking open and for carbon balls.
Also check IAC valve operation and clean it.

Does it have the electronic EGR valve?

No check engine codes or lights. Unknown as to the electronic EGR. Will have to pull cover to see. I had engine replacement done by a third party. I did have to pull the factory radio out, as the digital display remained on fully even with key in off position. Ran the battery down over a week or so of time, not driving it during that time. I assumed it was a defect with the radio, but wonder if it might be a window into other electronic issues that may be source of the stall/surge problems.

No check engine codes or lights. Unknown as to the electronic EGR. Will have to pull cover to see. I had engine replacement done by a third party. I did have to pull the factory radio out, as the digital display remained on fully even with key in off position. Ran the battery down over a week or so of time, not driving it during that time. I assumed it was a defect with the radio, but wonder if it might be a window into other electronic issues that may be source of the stall/surge problems.

Is battery voltage holding good and battery and charging system good?