We recently traded in both of our 2015 570 Sportsman EPS's for the same. With 3 hours on them, one misfires between 4100 and 4400 RPM's no-load or light load. No backfires, but close. The 2015's never had this issue. The other new ATV misfires less often and below 4000 RPM's. Gas is premium non-ethanol, plug wires tight, etc. Unlike many on these postings, we have a local dealership that is technically excellent. I took the problem one in to the dealership today, and it misfires the same as their new floor model. Mine: 4 hours. Floor model: 0 hours. It starts well, ALMOST backfires at the 4000-4400 RPM range with light load, but has no acceleration or other issues with the engine. The service dept is certain that the electrical is good, and fuel pump pressure is good. That leaves a fuel issue and "all 2020's are the same". Here's my thoughts: We're at 6000' elevation (though it repeated at 5000' at dealership) and running the best (slowest burning) gas possible. Am I experiencing pre-ignition? Or missed ignition? Should I try a cooler spark plug? Hotter one? Something else? More break-in needed? Thanks for your ideas!