im getting a real bad vibration when i step on the gas on my 91 explorer..the vibration stops when i let off the gas ... maybe a u-joint or a tranny mount loose??...any one point me to the right area? thks

by The Sounds Of It, It Seems Like You Might Have A Busted Motor Mount, But Then Again It Can Be Alot Of Things, Where Exactly Do You Feel The Vibration? Do You Feel It On One Side Of The Motor? In Front Of The Motor Or By A Tire? It Can Be A Motor Mount, A Transmission Mount Or Even A Cv joint

vibration feels like its right on your feet or through the middle of vehicle

I agree. Busted motor mount likely cause.

WHAT IT CAN ALSO BE IS A OUT-OF-BALANCE OR OUT-OF-ROUND TIRE OR WHEEL, IT CAN ALSO BE A LOOSE, WORN OR OUT-OF-ADJUSTMENT REAR WHEEL BEARING, ALSO CHECK THE SHOCK ABSORBER AND SUSPENSION COMPONENTS FOR WEAR AND DAMAGE, PEACE