If your state does not have emissions testing, cut off the exhaust behind the catalytic converter. Take a breaker bar or long hard metal object and poke through the cat. Keep doing this until all the guts inside the cat have been broke free. Start the truck and blow it all out. Put in a sleeve and some u-bolts. More power and will probably fix the problem. Had a van with this problem and I just ran a straight pipe. Problem solved.
VT247