I have a 2007 Dodge Ram 1500 w/ a 5.7L HEMI engine. The truck has been great up until 100,000 miles which happened last month. The biggest problem is that the A/C doesn't work when I am parked or at idle speed. It works fine when I am moving above 20mph. I live in Houston, Tx where it normally is 90 degrees with 100% humidity so this is a major problem! Any ideas before I take it into the shop and spend $1,000.