Chevrolet Repair: Camaro drivability - loses power, o2 sensors, high mileage

Question
97 camaro with 3.8 V6 seems to lose power after driving awhile. Injection system cleaned and fuel filter replaced. runs strong when cold. Popping sound heard when lots of throttle used in 5th gear at highway speeds - presumably raw gas igniting in exhaust system. Any ideas what might be wrong?  

Answer
You didnt specify but how many miles are on this car ? a couple of places I would look into is 1st if the car has high mileage you may want to have the catalytic converter checked, could have a blocked converter that would seem worse once the car is fully warmmed up, I would also change the O2 sensors if you have not already done so, DO NOT use an aftermarket O2 sensors as I have seen my share of problems with those, stick with original epquipment whenever possible. 1 more question are you getting any check or service engine lights coming on ?