Normmm the fan has the highest load on it when it is empty or no product in the air stream. It will be intersting what type of RPM you will get out of it when the product is in the air stream. Do you have a dual fan and is each fan driven by a different remote? If so do you see any differences in speed between the two fans? Do you know what pressure the tractor is putting out at 36gpm - could it be that you have flow but not enough pressure? If this unit is used could the hydraulic motor on the fans be shot?