See how the car runs with the plugs before you pass judgement on the Boschs.
FWIW, I've had Delcos, NGKs, Autolites, and Bosch's in my GTP and it likes the Bosch plugs the best. It was soggy with the rest of them (noticibly), and fouled out the Autolites pretty fast. I just changed BACK to Bosch plugs this weekend and the throttle response is crisp again. Same heat range, same gap each time.
