DodgeForum.com - New here with a stalling question

Hi everyone!

So I've been poking around lately and thought I would ask you all a question. I got the Ram I have now, a '98 1500 Sport with about 158k, just over two years ago from an old family friend. It had been sitting and was not running at the time, and I paid the price my friend would've gotten for scrapping it instead. So it's already been saved!

The clear coat is completely faded on the hood and roof and other spots, and the rocker panels and bumper were totally rusted away. Anyway, after several grand and numerous repairs to get her running and improve cosmetics, things have been going pretty well.

Issues crop up here and there, and one in particular last year has me puzzled. While driving at low speeds less than about 30mph, if I abruptly let off the gas the engine RPM drops to ~400, well below idle speed, and usually stalls as I roll along. I was able to get to my mechanic by just driving with two feet and all was well for awhile. I don't remember what he did (since other things were also fixed at the time), but just in the last week, the issue has cropped up after laying dormant for almost a year.

Any idea in particular what this may be? I'm still able to drive just fine so long as I let my foot off the pedal extremely slowly until it remains at idle speed, but any sudden movements and it will stall. Thanks for the help!