1996 Isuzu Trooper 4x4, 3.2L 6cylinder grinding feeling underneath my feet.

What is your question?

Just started doing this when I hit 40 to 50 mph, not sure what it could be. Any ideas? Also, it idels at a high rpm an takes a little time to gain speed. Slightly shakes, an when I push on the brake pedal it does like a shutter almost.