both those springs are very close to coil bind. i would have looked at going with a longer spring in the same 900lbs or 1000lbs over just upping the rate. unless you have done the math or want to post the math, put a zip tie around the the middle coil (not tieing two coils together, just around diameter of steel). next time you drive the truck, look at the zip tie. if its gone, broke or the plastic looks some what smashed on top or bottom, you are coil binding and have too much preload in the spring