i've got a 99 disco II. been running perfectly... now at 2025rpm i feel a mild resistance in the engine. once over 2025rpm the vibrations stop as well as under that rpm. the vibrations feel like engine breaking however at a cruising speed. does anyone know what this could be? an air blockage, or fuel blockage? it's been recently tuned up and i can't bear to drag it to the dealership again.