You need to have a way to test the fuel pressure with a gauge first. I tied into the port on the backside of the filter bowl with some extra fittings and a plain old repair shop style fuel gauge, don't remember what I used, but should be easy enough to replicate if you have a gauge available. see what your truck is running now for a base reading, then make very small steps when you shim the spring, some guys claim to be able to use washers, but I've never been able to locate any that would fit, I used a small screw that would fit into the spring, and ground down the head of the screw until I got the pressure to 70 psi, it took 4-5 tries until I got it right. Good luck
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