I recently upgraded to a stihl ms 391 but am having alot of issues. When I first start milling it ran great but about 20 seconds in it will barely cut. I have a 25" bar on it currently. I have a brand new chain on it and have also tried a few differentripping chains. Ive only used this saw a few times. At this point my 211c cuts way better. I understand a pro saw or bigger saw would be better but this is what I could afford so any help with this issue is appreciated. Any ideas? Thanks