I have a Sears riding mower 17 HP, 42" Model # 917/271661 and it has begun to cut unevenly.
One side cuts much lower than the other. I adjusted the deck height on each side so it cuts more evenly but now the whole deck is lopsided. By that I mean that the side that cuts lowest is raised as high as it can go, and the side that cuts higher is as low as it can go. What else can I adjust?

When was the last time you had the blades sharpened? This sounds very similar to a riding mower my son fixed a few years ago. The old geezer who had the mower brought it over and said the mower was eating holes in his lawn as it was cutting all wrong. He had taken it to the dealer and they wanted a small fortune in repairs to the mower. My son decided to try just sharpening the blades. Long story short - it was the dull blades. Mower worked just fine and dandy and the old geezer saved a ton of $.

I sincerely hope that this is your solution.

You hit anything big lately? Possibly bending the low cutting blade?I know with all the stones here on my property I hit either them or tree stump parts left over from yesteryear... bent a few over the course of 15 years or so.

Sharpening can also be the remedy,as Twinkydooter stated.With mine(a John Deere) even the thickest blades,once dull,can make the whole job look bad.

If you are handy enough, removal of the blades isn't too terribly bad(Just make sure the key is out!! ), taking the blades to anyone who sharpens rather than taking the whole mower to a shop,will save you a lot in labor.(yet,if it is something more than just blades,perhaps taking the entire unit in would be the right thing to do too.), Up to you:)