When first put in drive and step on gas, I get a clunk.

It sounds like you have a broken motor mount. I bet it klunks from drive to reverse as well. This is a common problem with the Taurus. Hope this helps. Doc

Sounds like one of the CV joints in an axle is bad. Check and see if it makes clickking noise in tight u-turns which is another indicator of a bad axle. That way you can see which side it is. I recommend replacing both at the same time.
The other possibility is that the motor mounts are bad. With the engine in drive and the parking brake on and your foot on the brake,open the hood and watch the engine as you give it a little gas. It should only move a few inches. If it jumps up and clunks back down when dropping back into place the motor mounts are bad.
You have to replace all the motor mounts as a set or the new mounts will be worn quickly from carryiing all the engine load.