I have a 2000 k2500 with about 85,000 miles on it. It is losing both oil and coolant, but I can find no leaks. There is no oil in the coolant, or vice versa so I do not expect a blown head gasket. About 400 miles ago my check engine light came on and a code reader indicated high engine rpms so I replaced the iac and truck ran fine. Then check engine light came back on and I noticed the disappearing fluids. Any ideas?