PTRich, i also have the 60 inch deck. I'm really not sure what the problem is. Since i can drive over the same areas, without the deck and not tip means its one of two things ... at least to my ay of thinking. Either the loader arms put down-pressure on the ground causing the front end to lose traction and slide down the hill, while the rear stays planted or the weight of the deck itself pulls the front of the tractor downhill. You can feel the front want to go sideways so of course you try to compensate by turning ,ever so slightly, uphill. But even if you don't turn uphill you still get the wheel lift. The tractors definitely still in float. Now here's the interesting part. Your driving across the hill when the right front wheel lifts up so you stop. So now if you pop the mower out of float, the loader arms really push down and raise the front of the tractor ... very suddenly. If while in the three wheels on the ground position you back up instead of popping the mower out of float, the front wheel lowers back down ... if you try to go forward the wheel keeps raising off of the ground till you feel like your gonna fall out of the seat and stop.
I've tried mowing going the hill. My observation is that the loader arms do not travel upwards easily enough to allow this. Instead, as you go up the slope the mower deck puts an increasing amount of pressure to the ground as the loader arms resist moving upwards until the tractor slows to a crawl and you give up. I'm sure if i continued it would stall. I've eased up on the treadle, to allow the hydrolics to catch up without success.
Please ... anyone that wishes to participate ... try this!
Heres a question i have. With the tractor at idle, sitting on level ground without an attachment. Try raising the loader arms by hand. They raise fairly easy and will drop to the ground when released... next go to full throttle and repeat the process. My loader arms don't want to budge. Is this normal operation for the rest of you guys???
The trick all this is to take the mower out of float and raise it up enough to drop the wheel to the ground and still be able to cut the grass. Monday i hit a spot where even this didn't work. Due to the curve of the ground in the drainage ditch, one side of the mower was cuttin air. So i attacked this spot from the opposite direction and was able to get past it. Very agravating to say the least.