I hope to get advice from members here. About 4 months ago Livernois Motorsports installed their LMS675 package on my 18K mile 2015 Mustang GT automatic. They also installed OPG/Sprocket at the same time. The car had some drivablity issues from the beginning. I contacted them within a few weeks from the install. Made a lot of torque/power, but backfired a few times. Would kinda jerk. I called them several times stating my issues. Took it there about a month or so ago and they kept the car for 2 weeks to drive it. Put 120 miles on the car and said it had a "random rev limiter" issue. I got the car back and it got progressively worse. I took it there 2 weeks ago. The salesman said the engine is bad. There is blowby in the crankcase. I don't live near there so yesterday after keeping the car a week and a half, we had a conference call with the business manager/calibrater/salesmen. They were respectful and seemingly straightforward. Bottom line is that I need a new short block or rebuild. Probably a bad piston/ring. They said the heads are likely good. They are saying I likely had a bad tank of gas. Is this possible? Tomorrow they are giving me a quote on an installed forged shortblock. I never raced the engine. Car ran perfectly before. They are saying they installed 75 of these exact setups in the last several years with zero issues. Any information you can supply will help in my decision to have them fix it or get the car back. They make a pretty strong case for bad gas.