Grrrrr.....I might be the wrong person to ask about this. The fact that I'm not a fan of GM does not fit well with the fact that I make my living building cars based around GM parts. With that said, I would say that about 90% of the problems I've had with these cars comes from problems with the GM parts.

The first car I built......had the engine (donor LS1) running multiple times for over a year in the GTM. Suddenly it would not start. That was the dreaded VATS problem....which forced me to spend a bunch of money on HP Tuners.

The second car I built was a new crate LS376......sort of. This was when the LS376 first came out....so to adapt it to the GTM, the owner had an engine builder swap out the 58 tooth crank sensor with a 24 tooth sensor so that we could run the C5 engine computer. The first start of this engine resulted in a large pool of oil on the shop floor. There is a cover on the engine block behind the flywheel. The bolts were only finger tight. This, of course, required pulling the transaxle and clutch and flywheel off and tightening the bolts for that cover panel. Put everything back together and restarted the engine. Now we only had a small puddle of oil on the floor. Oil pan leaks. Pull oil pan, install new gasket and put back together. No leaks. Take car to dyno. They can't get it to run right....car spent 3 days there. Found out all of the intake manifold bolts were only finger tight. Tightened bolts. Completed dyno tune. Drove it an ran it with no problems during test drive. Delivered to customer. Car won't idle. At all. Dies unless you have your foot on the throttle. That was about 9 years ago....so I don't even remember what needed to be done to fix it. We found a local tuner to come look at it, and I think he ended up changing the tune to fix it?

Next GTM we built had a Katech Street Attack engine. Katech supplied the entire package...engine, ECU, harness, etc. Took to the dyno tuners after the car was completed. They worked on it for 2 days and could not get it to not die when coming down from idle. Katech would not provide any help. Called them multiple times......you'd think that $29k would buy you some support.....apparently not.

One of the next cars we built had a stock LS376 crate engine in it. This was during the time when they had a rash of oil pick-up tubes with a cut o-ring. Before I installed the engine, I pulled the pan and sure enough, the O-ring was cut. Replaced the O-ring.

Since then, if memory serves, I've had a total of one engine that I've installed that didn't leak oil. Some leak a lot, some just seep enough to keep the oil pan damp. After working on 24 different GTM's, I've come to the conclusion that LS engines just leak oil....apparently this is just normal. If not, then I have the worst luck in GM engines.

In the past 5 years, I'd say I've had the best luck with just plain ol' stock GMPP crate engines. We've installed lots of LS376's and the 376 "Special" 525hp engines with the stock GMPP ECU provided with the engine. Use a single 4" CAI with the MAF sensor installed in the center of a straight length 4" tube. They all start and run and idle fine. They seem to be the most "turn key"....with no major drivability issues or absolute need to tune them. I'm sure a good tuner can squeeze more out of them, but at least they run and idle right out of the box. You might have an oil leak here or there, but for the most part, at least they start and run and idle.

flowtowngtm's car was the first and only experience we've had with Mast Motorsports.....and it also started, ran and idled great, right out of the box. Also the engine with the scariest amount of torque. The only GTM I've driven that I would't even think about putting the pedal to the floor in 3rd gear at 80mph. I've never experienced wheel spin at 80mph, but was fairly certain that I easily could have......and I never want to experience that.