[TTA850]

Since you can duplicate the problem sitting still it should be easy to find by someone with the right tools who knows what to look for. If it just started the last 6 months but was fine before then I doubt its in the tune, any time a car I've tuned started running a little off its been something electrical or mechanical going bad - sometimes you can tune around the problem for a while but in the end it should be found and fixed. Who did your initial tune? Maybe they can datalog whats going and give you a direction to go on cause changing parts blindly sucks.

-Steve