I have 17k miles in ~17 months on a GTM Stage 1 SC kit installed by a local shop. Other than several oil leaks and some cooling issues I have not encountered any serious problems.
I am also still in the stock clutch and CSC for now, but I do not launch the car either. Launching the car is hard on the clutch and just results in wheel spin on some expensive rubber. Not worth it IMO. But from a roll, the car is impressive.
I also eventually got a custom tune to eek out a little more power for 419WHP/350WTQ. The tune from Sam is pretty good though.
Here is a post I made a while back that might help. I would just tell you that proper preparation prevents piss poor performance. I am not going to tell you that you will get OEM like reliability with an after market FI setup but for me it has been worth the trade off so far.
GMT stage 1 or 2