I bought a new j/d lawn mower last year it has worked well, until lately, it doesn't cut uniformly, there are high "lines" down the length of the cut, I mean real noticeable! I tried removing and sharpening the blades, didn't change anything, also I have cleaned all stuck grass from inside the blade area, any ideas why this doesn't cut flat? Thanks for any help/tips...

Very sinple... your deck needs to be leveled. Read the manual for instructions on how to do this...

You should also check you tire pressure in all four tires, raers are the most important. 10psi is a common recommendation but check the tire sidewall. A big tire with 5 psi looks very similar to a 10 psi but really screws up the cutting. This will show most when cutting on a hill parallel to the slope.