I figured out the parts from Shurflo years ago and have been rebuilding the pumps myself with zero issues and they put out 150 plus. As mentioned its 20 to 40 bucks in parts and very easy.
Disconnect wastegate and go WOT and see if you get KR. That will help pin point a posible machanical false KR like a loose something rattling against frame or block and knock sensor picking that up.
Update... I'm putting spaghetti Engineering rears and fronts on my new GN and ran into issues where with the taillights would not work with the lights on as well as the blinker lights in the dash were on but dim. Tried adding 2 load resistors and the same. Did a quick search and it's been a few...