I dont know about the v6's but the LS1 seems very reliable, I only have 37K miles on mine, but about 30K of those have been within the last 12 months and besides replacing a power window motor I've never had to replace anything. I beat the hell out of it and its never skipped a beat, my LT1 when it was stock had minor problems, I had to replace the thermostat, and rebuilt a transmission with alot of miles, nothing major.....until 10lbs of boost got shoved down its throat. It was not pretty from then on.