My 2042 had the mulchers when I got it. It didn't cut worth a hoot, and would leave strips uncut in the middle. I told my dealer and he gave me a set of hi-lifts. I thought they would do the trick. To my surprise, it wasn't any better.
I always mowed in #6 position since it was the dry season and I wanted to give the grass a fightin' chance over the weeds. But then one day, I dropped the deck to 5 and it sounded like it spun faster. Odd, I thought. I just figured it had something to do with ground effect and when the deck was lower it had less resistance, or just sounded different.
Finally, I got to looking around at it, and noticed that the take-up pulley for the deck belt wasn't swinging far enough over on it's arm to take up the slack. The engine-to-deck drive belt was fine, but the other belt had slop in it that would go away when the deck was lowered to 5 and below. I took it all apart and greased the shaft (it's a half-fast design IMO) and put it all back together. Now it roars even at setting #6 and it doesn't leave any uncut strips up the middle.
Lower your deck as low as it will go, then raise it to 6 without anything running. See how much slop is in the belt that goes around the blade spindles. If it ain't tight, you have the same problem I had.
Good Luck!
