Check a couple things...
On the Deck, Are all the hangers and supports attached and UnBent?
With the mower parked on flat & level spot, check the blade tip height, front and rear & left and right, obviously you will have to turn the blades to face the front and then turn them 90 degrees for the side to side measurements.
all the blade tips should be at the Same height with the blades set from let to right....
But with blades set Front to Rear... the Front tips should be around 1/4 to 1/2 inch Lower than the rear....
Since you are having scalping And an Uneven cut ... I suspect your deck hangers are having some type problem... KennyV
