I just bought a new fan clutch (Hayden Model 2797 "Severe Duty" for rear gears 3.73 and higher) for the K5. The truck really makes a roar now. I've got the SM465 so that is to be expected but seems almost like too much. I wondering if I will start to lose fuel economy, power, etc. They have the heavy duty version (Hayden Model 2747 for rear gears 3.42 and lower) but I wasn't too happy with the way it would bolt on to the pulley, which is why I got the severe duty one. I have 3.42 rear gears. Any ideas??? I'm thinking of taking it back and getting the heavy duty model instead. I must say though, it sure is keeping the truck cool. Truck stays right at 195 now even with the A/C on in stop n go traffic in close to 100 degree heat.