Just like the title says, my S40 stalls when I'm on the highway, usually after 1 or 2 miles, or even going fast (~55 mph) in 4th, as I found out today. Throughout town, she purrs like a cat, but I can't figure out the stalling. The only thing I've done to alleviate this is run some Seafoam in the tank. But it still stalls. Any ideas?