OK. 1991 Dakota, V6. 215,000 miles. First- New cap, rotor, plugs, wires. All correct items. Champion plugs are clean and gapped correctly. New fuel pump and TPS. New PCV valve. All the vacuum hoses are new and tight. Cleaned tank with Sea Foam as well as throttle body with TB cleaner. Timing is correct and no noise from chain tensioner (may have already been changed out). Oil is clean with no sign of head gasket issues. The problem - Truck is incredibly sluggish. Floor the pedal and it gets moving...just barely. At partial throttle, it will cut out and "misfire" (not sure it actually misfires, but it will backfire slightly). Poor fuel economy all the way around. To really get up to speed, you have to floor it. It will downshift but not stay in the lower gear. It upshifts again too quickly for the lower gear to be any use. Does this sound like a plugged cat? With 215,000 miles it could be. Not long before this started, the truck backfired big time after a cold start in about 32 degree temps. Would that have blown out the cat and plugged it up? It idles fairly well at the correct RPM, but not strongly. Any ideas or suggestions.