190 degrees Fahrenheit is not hot enough, and it's definitely not broken in. You should be running at least 220-230 towards the end of the break in period. lean it out just a TAD, and you'll notice a huge difference. Also, if you're not preheating your engine, please keep an eye on the lower part of your conrod. cooler running temps, new motor, and starting cold may accelerate the wear on the lower end.

Shims. Take out the copper one and run two aluminum ones. This goes for all three GX engines.