I purchased a GC2300 this spring and have had the dealer come out to my house and then he came a got it for the same reason. The deck is not level in the up position and tends to be unlevel when lowered. The dealer removed the pin on the left side and used a roll pin to keep the lift arm from moving on the shaft. This worked great, until you set the deck with the adjustment. I removed the pin on the right side and got a roll pin to replace it. This really made a big difference. The problem with the deck is than the adjustment is on one side and the lift arm is on the other side. When you set the adjustment the lift arm lowers until it hits the stop on the adjustment, with the factory pins there is to much play in the pins and allows the deck to move more on one side then the other. I do not run the deck wheels on the ground, I leave then up about 1/2" - 1" above the ground. So far replacing the pins with 1/2" roll pins have solved the problem. One thing to keep in mind is that the holes in the lift arms on each side are metric, I used a 1/2 drill bit and drilled the holes so they were the same on the shaft and the arm. I could not find a metric roll pin and a 1/2 is to big so you have to drill out the holes.
I also read an message about running out of power going up hill. Due to the tractor being hydro, if going up a step hill you will more than likely run out of pressure in the transmission. If going up a step hill shift into low range and place the tractor into 4X4. /forums/images/graemlins/wink.gif