I just got a nelson tune for the 44# injectors i just installed. I also had TR6 plugs installed previously and asked nelson to tune it for TR5's since i no longer plan on running nitrous. Well i got my tune in and wanted to be able to run it, but i couldn't find NGK plugs anywhere (except online) so i called the GM dealership and just went and picked up the ACDELCO Iridium plugs that go in the stock 6.0l's. I then started it up and the idle was much rougher than the first tune i got. It kinda surges around from 500-900 every now and then and then will smooth out. So i thought i'd take it for a quick spin and it ran fine at low rpm but if i went WOT it started missing really bad so i just let out of it and took it back to the shop. What do you guys think is the problem? Is it not safe for me to interchange the AC's for the NGK's? Thanks alot