2000 PONTIAC TRANS AM Engine Problems

TROUBLE CODE FOR BAD CATLIC CONVERTERS THE HAS BEEN REPLACES 3 TIMES PRIOR AND NOW THERE CLOG FOR THE FOURTH TIME? ASKING GM TO REPLACE AS A WARRENTY ISSUE SINCE THE LAST TIME WAS 4 YEARS PRIOR AND I WAS TOLD THAT THE NEW ONE WOULD BE COVERED FOR 10YEARS 100000 MILES DUE TO GM WARRENTY POLICY. SECOND THAN IS THE CAR HAS DROPPED IN GAS MILEAGE FROM 26MPG TO ABOUT 14 BOTH HIGHWAY MILES. AND THE LAST THING IS THE IGNITION LOCK SOMETIMES WHEN I TRY TO START THE CAR THE SECURITY FEATHUR SUCH THE CAR DOWN DUE TO THE ANTI THEFT CONTROL. I AM THE ONLY PROUD OWNER OF THIS VEHICLE AND WANTED TO PASS THIS CAR ON TO MY SON AS A VINTAGE TRANS AM WITH ME BEING THE ONLY OWNER BUT WITH THE ISSUES THAT HAS BEEN GOING ON I MAY BE PASSING IT TO A...