I have a 98 f-150 4x4 v8 4.6L, when i put it into reverse it makes a loud clunking noise, shakes the whole pickup. I have to hold the brake for a few seconds and wait for it to engage to reverse, if i dont hold the brake and wait it just shakes terribly if i give it any gas whatsoever. It works just fine in any other gears, just reverse does that, any ideas what it could be?