I keeping finding new little problems with the 2000 ext cab 4.8l truck I recently purchased. The latest is if I turn the heat up even a little it just keeps getting hotter and will not turn off. When I come to a stop I can hear a motor or valve or somethhing under the dash which is trying to move and sounds like a gear slipping. After turning the truck off and restarting the heat will go back to cild an stay that way until I move hte temp control again, Any ideas? Thanks for any pointers in the right direction.