I'm having a possible clutch issue that I need some help troubleshooting. When I first start the bike, I put the bike in first gear and released the clutch to get the bike going, it feels like the bike is not completely engaging in first gear. The acceleration of the bike is very, very slow, and it feels like the bike isn't fully catching first gear. This continues to happen moving to 2nd gear, and I can't really go past 2nd gear as the bike is barely breaking 40mph at this point. I have already adjusted the clutch cable on the handlebar and on the bottom of the bike to allow for more clutch engagement. I've read on a few forums this could either be the clutch plates that need to be resurfaced or a leaky transmission seal that's dripping oil on the clutch, causing it to slip. If I ride for about 15-20 minutes or so, the problem vanishes about 95% of the time. Any help is appreciated.