Duh! I guess that makes sense, that part about
"If the back wheels can't spin at different speeds, you go straight!"
I'm not sure traction is the issue in my case. I went with the garden tractor to help clear and level my land (as I just moved out to the sticks). Lots of rocks, construction junk, and stumps (from saplings to the huge & fug-ly monster pines). I'm slowly working my way through it by hand, pulling the stumps and moving rocks.
I then rig up the rear grader blade, hop on the tractor and do my best to level the land around the craters left from that stuff. At low speeds the tractor often gets stuck whenever either wheel hits a low spot.
If I crank up the speed I don't get stuck as often, but the trade off is that when the grader blade gets hung up, it's a jolt like you wouldn't belive (I need an air bag!).
As said, i'm learning as I go and I'm gaining a technique. Biting off smaller chunks and slowly circiling low spots. I've lost 3 clevis bolts from the sleeve hitch in the dirt : (
So, I got some solid 3/4 in nuts and bolts and replaced the Clevis bolt/cotter pin setup. Those bolts ended up vibrating loose!!!
So I tightened them down (only so they were sort of snug) and sealed up the end with some liquid steel from wal-mart. Haven't had a problem since.