2008 Polaris Sportsman quit
Unfortunately for you it sounds like a bad ECM, or electronic control module which is basically the brain for your machine. My 2007 Sportsman 500 has went through 3 of them, luckily for me mine have been warrantied. The problem is where they are mounted, there is little protection from dirt and water.
I also had fuel injection wiring harnesses go bad more than once, but the machine still ran and functioned, it just backfired a lot and lost power.
Good luck. FD
Trade ATV into the same dealer for a used or new one. Try and make a deal with the shop that you will change out the harness, but if that's not the problem, they will trouble shoot it further for free if that's not the problem. You would then be stuck with the harness, but they did say they had problems with the originals anyways. It's a tough call because you need something dependable when it's cold out there. Good luck, and maybe someone else has some ideas.