My 54" MMM seems to leave a row of partially cut grass right in the middle. I have sharpened the blades and the alignment seems good. I have noticed that the problem is worse in turns. I admit that I mow quickly but the problem is only a little better when I slow down. I was at 190 RPMs on the PTO this morning, and the grass was a little high. But it just appears that there is a coverage problem of some sort in the middle, where there is no overlap. The problem diminishes when I go over the same area again (cutting less grass). Solve this problem and you'll be the recipient of a coveted polite round of applause.