2002 Chevy Monte Carlo Misfiring

My car was recalled this year, so, I took my car to the dealership. They replaced the spark plug wire channel with new spark plug wire retainers. The following day my check engine light came on. I took my car to autozone & got the diagnostics. It stated that my car was misfiring. So I took my car back to the dealership & told the service rep that my engine light came on the following day after their service tech had replaced my spark plug wire channel. The service tech recommended a diagnostic test, in which, the charge is $90. I told him I'll get back with him bcuz I already had a customer rep diagnois my car. So, I would like your opinion. Do you think the spark plug wire retainer is causing my car to misfire?

Note: My car was running great & the check engine light was off.