I have a troy built ltx1842 lawn tractor, I can not get it to cut even. When I have it on a flat surface I can put a level across the blades and they are even. But when I am using it to cut grass it cuts low on the left side. The tire pressure is 10 lbs in the rear, 14 in the front.

You could have bad spindle bearings, or you may have a warped/ bent blade. Or the blade may not be placed on the spindle correctly, make sure the blade is up onto the "star" of the spindle.

Check the blade balance.

The Redneck way:

Take a round shaft screwdriver and place the shaft horizontal in a vise.
Place the center of the blade on the screwdriver and see if you can balance the blade. e.g. no hands.

Also take your tractor and place it on a flat surface like a driveway and measure the distance from the blade to the driveway in 4 positions (0, 90, 180, 270) and compare,

Make sure the engine can't start by taking out the plug and/or disconnecting the plug wire.