Got this bike about a month ago. Had to replace the battery, the clutch cable and just did an oil change. The past couple days I've been riding my bike, once I get in sixth gear and start hitting 6000 rpms about 50-55 mph the throttle will quit giving power to the engine and start slowing my speed and rpms down. Then when I pull in the clutch to shift down a gear the engine dies, once i release the clutch it kick starts the engine back up. I thought it was overheating so I'd pull over and let it sit for a minute and then start it back up, but it will only start on choke. If I try and change it to run it will die. After a while it'll start back up and run just fine, without choke. But if I get it back in sixth gear and start hitting those higher rpms it will start acting up again. Any ideas to what the issue is? I was thinking maybe muffler clogged or carbs need cleaned. Even thought about changing the air filter box to just single pods on each carb.