I currently have a 2009 F550 4x4 141"wb. I love the truck but I hating the 6mpg that the 6.4 is giving me, I am also starting to really lose faith in the truck. It has never let me down but when it regens every 40 miles I know it is coming. I also have a 2002 QCSB and LOVE it. My question is what besides the motor and trans are the differences in a F550 with a 7.3 vs a 6.4. The 6.4 will out turn any vehicle on the road my 7.3 sucks do all F550s turn tight or just the newer ones? I cannot imagine the difference being too extreme, but as the 6.4 was my first Ford I really do not know. I only got the 7.3 in Feb so I am still learning.