I have an L553 with 1020 hours on it. always worked fine but when i was travelling it started surging and bucking. I tried more throttle, less throttle, and nothing seemed to help. If i go really slow it doesnt surge. bucket seems to work fine. I thought maybe it was clogged filters or screen, so i changed them and cut the big filter apart and there was like a little bit of a metal shaving paste in the pleats. i assumed was from normal wear. Any ideas what it might be, or a way to check what it is.? thanks