2000 magnum

When the cat plugged up on my 1999 Ram 2500, it sounded normal but felt like it was pulling a 10,000 lb trailer all the time. Didn't realize it was losing power until it got pretty bad. Replacing that cat really helped, but that truck never had impressive power.
My current 99 Ram 1500 is not programmed for the tire size, but I did program the 2500 for the tires right after I got in about 2001.
For comparison, my current primary truck is a 2008 Ram 1500, four wheel drive, five speed auto trans, and 100% stock, including tire size. The 5.7 Hemi with cylinder deactivation still only gets 15 mpg at 75-80 mph. I checked this one once at mostly 60 mph on a long trip and it was averaging 19 mpg for a few tanks of gas.
You'll get run over if you are only going 55 mph on southeast Michigan freeways.