Welcome to your V Strom! There is a crazy amount of information on this form. As for your 3500 rpm backfire, could be fuel or electrical. Initial thought without more info is a throttle body out of sync or “lean” condition problem if every else seems to run fine. A throttle body sync is pretty easy to do, check out You Tube. Also, the intake boots can crack and may start to leak over overtime causing it to run lean, pop and backfire. Fuel filters get clogged which might cause loss of power, but the symptoms are a little different. Also, the rpm range you’re describing is the classic clutch “chudder” rpm range, but that’s more of a vibration issue not really a loss of power or backfire issue, there’s a cure for that (Werks basket). Anyhow, I’m sure you’ll figure it out, chances are it’s something someone has fixed before and posted it here. It’s a great bike! Best wishes.