great job...
fresh spark plugs should make a lot diferent especially if your old spark plugs are worn out..
But what do you mean by the sparkplug comes with the coil end..???
As I understand it the coil-end is needed to distribute the electricity to the plug (sort of splitter) since the I-6 engine only has 3 coil for all 6 cylinder (unlike BMW I-6 individual coil for each cylinder bank)..
Regardz,