When do you guys determine the appropriate time to replace your secondary springs? Do you have a set mileage you change them, or do you monitor the performance? I have over 9,000 miles on my current spring and I'm noticing a 200-ish drop in RPM and a loss of 10 mph. The drive belt is new, the engine and driveline are healthy, and the primary is tip-top...been through all of this. I assume a weakened spring would allow the secondary to shift too soon and pull down my revs?