Q - when motor is run hard the 16lb. radiator cap releases and allows coolant to run into the reservoir and overflows. We have put a pressure gauge in line and found the coolant system pressurizes to 20lbs. when turbo spools upand kicks in? we have had egr valve, head gaskets and turbo replaced recently and truck was fine for about 6 months and we cannot come up with a solution. Possible solution?

A - Hate to be the bearer of bad news on this one, but most likely your head gaskets are leaking again.  When the boost comes up so does the cylinder pressure.  This when the head gasket issues usually show up.  I would also double check the egr cooler to make sure it isn't leaking exhaust pressure into the coolant system first though.  If it is not leaking, the head gaskets are.