Having a lose of power issue when using a 5' Bushhog with my L2900. I can work for 2-3 hours and then no power to the point of shutting down. Able to shut down throttle, PTO, and get it to idle, but nurse it back to the barn......Fuel filter has been changed. Oil filter has been changed. Hydraulic Fluid is full. Temp Gauge reads normal.......Preping to flush radiator and do not see a Thermostat in the part diagram........Anything else I should look for, check, test?