Its very strange to me that your having problems, although its a 66" and not the 60 I had. I never had a problem with lines etc unless I was taking a lot off. We cut similar lawns by the sounds ie bermuda and buffalo etc. I guess the irrigation isnt helping but even still, with the rain we get its the same thing. Is there any chance you could get the lawns shorter like 2.5", and keep them there? I would still see if you can get some of those off set blades but as you mentioned, they may not be easy to find.