I have a 4040 open station, powershift tractor with a 148 loader. Moved snow for several hours a week ago last Monday and worked perfect. Tried to move snow 2 days later and the loader worked but raised slower than normal, then in about 10 minutes would hardly raise at all and the three point raised slower than normal, but still drove and steered. This was when it was in the negative 20's and 30's here in eastern Iowa. Waited until this Monday when it was around 40 and it worked for about 5 minutes then would not hardly raise. Drove to the local shop the next day after starting the tractor and getting the bucket up. Drove it the 10 miles and it worked perfect. The shop worker pushed snow with it this morning for 30 minutes and it worked like it should. What the heck is going on?