I have a gc2300 that I am running 15-w40 Rotella in. It's wierd everytime the tractor get warmed up good, after about 10-15 minutes of using it, the oil pressure light flickers on. What is really strange is that it only comes on when the front end is pointed down hill. As soon as I turn up hill it goes out. Anyone ever have this happen or know what could be wrong with it?