The M100465 does nothing for whistle on a 6.0. It will be super quiet wop though. Seems almost like the more you push the throttle the quieter it gets.
I would recommend getting this. https://www.strictlydiesel.com/p-2804-obs-fuel-pump-harness.aspx You could probly do it cheaper but its not that ridiculously priced and makes it look nice and concise.
I'd say try dropping the pressure a little more and put a bunch of weight in the bed and drive a bit and work the sidewalls some. That being said i had a set of tires that i put on just before a trip and they felt sloppy for most of the trip or about 2000 miles. After i hit some curves and...
I don't know exactly how it works but If it was only getting half the signal at 3000 rpm wouldn't the shift box only be seeing 1500 rpm? I'm wondering if it was for some reason seeing twice the signal. Maybe you have it fixed and working properly already.
I tried calculating out the length of bar needed and have heard someone else say, i cannot remember who or where, that the bar needs to be about 12 feet long, to nearly exactly follow the arc that the axle moves back when the spring compresses.