I have a 2012 impala LT I want to buy a tune for I’ve been reading a lot on the benefits of the overkill and trifecta tune I am leaning more towards the overkill tune for its expandability over the trifecta tune.My question is, if I buy the hp tuner for 300. Bucks with 0 credits from Summit how many credits do I need to run the Overkill tune? Or do I need credits? I don’t understand what these credits really are. Any help with this question would be greatly appreciated.