Clunking noise from the rear end when slowing down
 

2007, crew cab, lariat,5.4, 119,000 miles. Recently had heard noises coming from the rear end while driving at slower speeds > 10mph. Looked underneath to find pinion seal leaking. Took it to the local shop to have seal replaced. While there they told me the noise was from rear brakes and emergency brake cable. Had leak fixed and brakes. 2 days later while stuck in traffic (going 5mph) and not touching the brakes the rear end felt like the brakes were on. Kind of a rubbing feeling. yesterday while stopping the truck made clunking noises at about 5-10mph. I can only repeat the problem after the truck has been driven for a while. The mechanic today replaced the rear end fluid and added friction modifier. While driving home it did it again while applying the brakes at slow speeds all most to a complete stop. The mechanic did mention maybe replacing the clutch pak. Anyone have a problem like this. I was told there isnt a slip yoke. Any help would greatly be appreciated.