Chevrolet Repair Questions? Ask a Mechanic for Answers ASAP
From your description of the problem, the catalytic convertor could be the problem. The easy way to find out would be to check the backpressure of the exhaust system before the Catalytic Convertor. You will need a backpressure testing tool to perform this diagnostic.
The only other issue that I have seen on these vehicles is a bad fuel pump. You will need to obtain a fuel pressure tester to perform the diagnosis.
If you have access to any of these tools, I can walk you through the diagnosis and give you the appropriate specifications for each test. Please let me know how you would like to proceed.