My 97 Land Rover discovery starts acting up once it warms up....such as, misfiring, backfiring, no power, can't go over 40mph down hill, barely goes 10mph up hill. After 40mph, when I push on gas pedal it does absolutely nothing. The same effect you'd have if You just weren't pushing it at all. Once it drops below 40mph the gas pedal registers again...... Any suggestions?