My TR86 would go 4.6 MPH in second gear. My TR99 goes 3.8 MPH. My TR86 would go 8.6 MPH in third gear. My TR99 goes 6.9 MPH. My TR86 would go 20 MPH in fourth gear. My TR99 goes 15 MPH. Why are the bigger machines so much slower? Other brands of combines have a higher road speed. Is there anything that can be done to increase the speeds on this combine?