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?

 

well other than a tune up....the first thing that comes to mind is the VSS ...vehicle speed sensor....is the speedometer whacky when the truck is running poorly ?, also check the fuel pressure ( to evaluate the fuel pump and/ or filter) you should have 30-35 psi at the check-port on the passenger side of the fuel rail....let us know how it goes