Hey guys, thank you all so much for sharing your knowledge in my case. I found the issue and fix the problem yesterday. While mowing I had the instinct to put some pressure on the gear. I notice that it cut better, so I stopped and followed the engaging gear. I saw that I had some adjustment and I adjusted the gear to pull more. To my surprise it fix the problem. Now my belly mower is working full power and I'm able to do the tast much better. As I said, thank you all for your help.