Update: I went back out today and the same was happening, but the tractor was on a slight down hill and the back wheels started to lift. Had it happen a couple time more. Sometimes the back wheels would lift and other nothing. I think the snow is just frozen harder than I had though and the relief on this tractor is not very loud when the tractor is at 2000 rpm. So at least in my case I do not believe anything is wrong, except operator getting used to the equipment. A little disappointed the loader is not a bit more powerful.