The 6.4 is not a bad engine/trans combo. Probably the best one they ever came out with IMO. At least for out of the box fun that is. Everything else about the truck sucks as far as I am concerned though-especially working on it!
I ran a brand new 6.4 bracket racing a few years ago and beat him with my wimpy 13.2. He had some sort of SCT tuner, stock trans exhaust, intake. I just had EFI exhaust/intake and a converter. Rest of the trans stock. I went to the finals that day, he broke after his second pass. Nuff said. Was impressed how fast it ran with just a tuner though. First time I ever saw a Ford run a low 13 with so little done to it.