There are several things that can cause your problem. Bent front axle, or worn axle bushings, Bent deck suspension arms, or deck hangars , Bent frame, sprung deck housing. May be one thing or a combination of several things.
Sorry, I just found this in my spam file. I'll check these out. I did find one major issue; one blade was installed upside down. That was the one my neighbor screwed up. Still it was my fault for not noticing. Still, the deck, in it's highest position, shows almost 5" on the inch gauge. But it doesn't cut that: it's about a 2 1/2 " cut. Anyway, can this be narrowed down? Thanks for your help. frank (the diy faux mechanic).