F525 front mower problems

I have newly sharpened blades on my F525 and have the side discharge chute held all the way up with a string. Infact, I just put the blades on today. I mow when it's about 3 inches high and cut it down to 2.5 or 2.75. My grass is dry because it was hot as the blazes here in mid-Michigan today. But for some reason, it leaves my lawn looking like a cut and raked hay field ready for baling when I get done. Both of my local John Deere dealers have told me that I can get a mulching kit, but one of the dealers told me it would be worse than without. I mowed half of the day with the dull blades, switched them with correctly sharpened blades, and mowed the rest of the day. However, there is little if any difference in the condition of the blades. I run at or near full throttle, my belt is in good shape and not slipping. I also travel fairly slow for the grass I'm cutting. Come on, John Deere wouldn't put there name on something that always operates like this! How can I resolve this problem? Thanks guys.