Your impeller could definitely cause problems if it dinged up real bad or even warped, are you able to take any pictures and post them here? Are you sure there isn't anything stuck further up there that could be impeding the proper speed rotation of the impeller?
If the impeller is in really bad shape you should be able to pick up an aftermarket one from Solas, http://solas.com, this impeller should also give you a little better performance.
Sep 17/08
I will try to take some pictures (if possible) this weekend, as I should be able to put it on my boat trailer (as there is restricted room on my marine railway to manouver) & will post them
- could it also be indicative of damage (or age) to the Wear Ring ?
- if I travel at low speed to get to the public boat ramp, do I risk any damage to the motor) ?