96 formula m6 has 140000 miles on engine, has new ignition system, has bosch plugs with 10000 miles, new fuel filter. Car pulls hard till 4500 rpms and then begins to miss. Any ideas? Some say bosch plugs are problem.

 

Honestly, I would say its the bosche plugs. I had them on my car and it had problems after about a week, just like your having. Except, i only got about 1000 miles out of them. It just got worse and worse, to the point where the car would backfire slowly taking off. There is a technical reason why the Bosce platinums dont work real well on these cars, especially the +3s. I would try using a set or normal plugs. And i would go back to stock wires, if your not running them already. Sometimes the best way to go is to get back to factory specifications untill the problem is cleared up.