Joe,
I ran 104s on my stock 98 GTP (Hogan DP,alt mod,ecm reloc, Denso O2,cold air )
Mainly wanted to try then as i had them on the shelf. Idled fine and ran great. Some guys suffer from poor gas milage with the cold plugs mine didnt. I would regularly get 16-18 mpg city. On long trips easy 26 mpg