Ok this has me scratching my head . When I started mowing this spring I noticed a low spot in my trail . One blade was cutting lower than the other. Bent blade was My first thought. It is doing it on a single cut across level ground. NEW blades , some result ! If it was not matched up when I take the next swipe I would think the deck is unlevel. I checked it anyway . Level. Tire pressure the same on both side. Spindles seem to be in good shape. It's almost like one blade is tightening up higher on the deck. Took them off switched the blades , still the left side...

If you can get it up on a rack of some sort check to make sure the blades are actually level with each other.

I know you said the deck is, but check the blades too. I bet your left side is sitting a little higher.

possibly a missing spacer or bad tension washer above the blade between top of blade and spindle making one blade go higher than the other?

Low tire?

My craftsman had a cracked spindle.. And from Sears a like $60 part but aftermarket $7...

Check the bearings on the spindle that is lower. The old cub cadets would do that.

I struggled with that exact problem almost all summer and it was always a different issue. I'd get one issue fixed and the next week it would have a new issue. One week it would have a low tire, then the bars that the deck hung on got cocked, then a blade was bent, then the front deck bar got cocked, and to top it all off, the bracket that the bars attach to on the deck broke at the welds. I got them welded back on and reinforced, and by the last few mows of the summer, all was well.

Just what Drifter said.

Check the rotator splint.

Tha was the first thing I did after putting on new blades didn't solve it. Seemed fine to me . No play and spun pretty easy ...

Im just happy if my mower starts!

You may have hit something and bent the deck itself, dad did that and didn’t realize it until the deck started to crack.