2000 chevy silverado pings?

My 2000 pings took it in for some maintnance and to complain about a trans fluid leak about a year ago. Mechanic charged us 1800 for some repairs and a 100,000 mile tune up, but couldn't find a leak. It goes through fluid like crazy. Then developed a ping. We stopped driving it while saving to have fixed. My... show more My 2000 pings took it in for some maintnance and to complain about a trans fluid leak about a year ago. Mechanic charged us 1800 for some repairs and a 100,000 mile tune up, but couldn't find a leak. It goes through fluid like crazy. Then developed a ping. We stopped driving it while saving to have fixed. My husban thinks maybe blown head gasket. Any ideas??? We haven't drove it since June.
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