I have a '03 F-350 6.0 lately when coming to a complete stop there like a thud right before i stop what do you think it could be I feel something bumo in my seat

 

I copy and pasted this from another thread, storm originally posted it, not saying it is what you are experiencing but look into this as it could be your problem and solution.

Rear Axle Slip Joint

1. Remove Axle from U-Joint clamps (be sure to mark orientation with chalk, paint)
2. Gently use needle nose pliers and spread the metal clamps (if done properly you can reuse them, no need for Zip Ties)
3. Remove Axle side of drive shaft slightly from the slip joint. Use a punch tool and make a small mark to note alignment. Use the blue Teflon Shaft as a point and the Metal Housing of the Transmission side Shaft to mark.
4. Clean Teflon Shaft and inside of Slip Joint on Transmission side Axle
5. Apply a nice amount of Grease (Schaffers, think thats how it's spelled, makes some DAMN GOOD lube. I used their Red Tube and so far my shaft hasn't made a single knock. By now the Ford stuff would be gone and I'd have the clunk).
6. Align shaft into Slip Joint and slide back in. If using Schaffers you will have a lot of resistence.. Just work it in and out (quit thinking dirty!) to get the lube in every spline.
7. Slide rubber boot back over Slip joint and apply the metal clamp. You will see two hooks on the end of it, slide it onto those hooks and compress the clamp point you spreaded in Step 1.

 

You can also use marine grade blue grease. It has water proof fibers in it and will probably last a lifetime.