Slim Jim was originally made by Goodmark Foods and sold out to Con-Agra in the 1990s. There was a total change in production and management. This could explain the change in taste.
I work in Raleigh, NC near the original Slim Jim works and once responded to an emergency response call about a Slim Jim spill. Chatham Dog Food Co. makes a locally famous brand of dry dog food and one of the ingredients was the cooking juices from Slim Jims (along with out of date non-sweetened breakfast cereal). Early one cold morning, a tank truck loaded with 8000 gallons of still warm cooking grease overturned in the middle of downtown Raleigh. Although rapidly harding in the cold, the grease ran like lava into a nearby office building. It ended up about knee deep, treeing the buiding’s workers on their desks. Luckily, I had a pair of chest waders in my truck. Somewhere I’ve got a photograph of a very disgusted fireman wading through the grease carrying out a fat lady piggy-back. They never got the odor out of the building.