I have done a fair amount of running under power in my 320 and I am surprised at how slow it goes. It takes real effort and rattle to even keep it at 6 knots. The problem is compounded by the fact that my throttle refuses to stay put and is always sliding down until RPMs hit 2000. The dealer said he tightened up the linkage as much as possible but it hasn't helped. On the boats maiden voyage, I got a fair size branch (nearly log size) caught behind the keel while wiating for a bridge to open. The log eventually worked its way out but not before an ominous THUNK was heard. Is it possible that I bent the prop or <gulp> even the shaft and that accounts for my slow speed? I do not have any water in the bilge so I couldn't have bent it too bad. The boat consistently sails at over 7 knots so I know I'm not hitting hull speed at 6. Any advice is deeply appreciated.