The "bump/clunk" in the drivetrain goes all the way back to 2005 (at least) as my '05 Lariat Screw 4x4 had the same thing. At that time I was told the driveshaft to transmission splines were binding and the dealer would drop the driveshaft, lube the front splines and reinstall. This fix would work for 5K to 8K miles before the lube would wear out and it would start sticking/clunking again. I haven't noticed much of this with my '09 - but my '05 had it bad. I finally just got used to the driveline "clunks" at 1st acceleration and lived with it.