I have an 05 chevy duramax lly eng. I have two problems. The first is the engine keeps puking out coolant out of the overflow tank. I replaced the 2 thermostats and the coolant sending unit as well as the overflow tank cap. all parts were oem parts. Do i have a blown head gasket or what? If so, how can i test this? The second prob is that my high idle is not working. I dont have a user manual so i dont know if my duramax even has an high idel. This is my first diesel truck. The mornings here have been in the low teens. i do plug in the block heater but doesnt seem to help much.