I just recently got my friend's Blazer through a trade. I mainly got it for the new SB400 with only about 2-3 hours of run time on it and hardly any miles. They couldn't run it for very long at a time since it would always overheat. The 1st intake they had on it was a warped aluminum Edelbrock performer, now it has a stock style aluminum intake. It's still heating up too much. Within a couple minutes of starting it from being cold, the water is just about boiling (sounds like it). It is .040 over with flattops, has a brand new radiator. But I'm sure the timing is off and someone said there must be a vacuum leak. What else could make it heat up so badly?