I play golf with both the sales and the service mgr. of my local dealership and have had the old tuner discussion. First of all, the service mgr. does not care if there is a tune installed, plus with KRC Performance in this town, they are well used to seeing modified trucks and unless it's either A) crazy high end modified or B) the modded part caused the problem, it's never an issue. I was told if I ever bring my truck in for work, warranty or not, just to let the writer at the desk know there is a tune on it so they will not try to do any PCM updates to it. Also, he states that you can only see a time/date stamp whenever the PCM was written to last. So if you return it to stock they can tell that the PCM "changed" recently, but have no way of knowing or proving what changed it. They'll basically know what you did but can't really prove it...