missing when cold under load

Hey everyone. Got a sportsman 800 2013. Just recently its started to miss when cold. Runs smooth at idle and higher rpm. It stumbles when its cold and i start lightly riding. It hesitates and stumbles a bit. Ive changed plugs and wires. Air filter is new. Ive tried searching both google and the forum with nothing close to what ive got going on. Never had an issue till just recently.