I have a 2000 721d with a 61" deck and more times then most I have to almost slow down to a crawl to get through grass that my JD rider would cut right through...I always sharpen the blades and mower is up to date on services and has around 1700 hrs on it..I don't know if it has to do with the older style deck or not but I thought that with a 21hp diesel motor it would pull through anything...anyone else have this problem? or have any suggestions?