Even Worse Starting
I also have an '04 6.0 L, but it's an F350. The truck has about 135K miles and has had issues with the injectors and mass flow sensor and the injectors were replaced under warranty just before the warranty was up at about 96K.
Starting is virtually impossible, right now, unless I plug it in (block heater, etc.) for a good 3 hours. I have tested this many times at garage temp (right now, about 55 deg F). Without being plugged in and just at that temp, I was able to crank like yours for about 30 or 40 seconds and get it to start, but I can't even get that to happen, now.
However, if it's plugged in for 3 or 4 hours, it starts right up. It runs rough for a while (maybe 5 or 10 minutes), but then runs pretty normally.
If anyone has any ideas on my starting issues, please let me know. BTW, I hooked up a scanner and show NO CODES. I also used the gauge to read water temp and intake air temp. When the truck is unplugged and cooled to garage temp (over night), both water and air temps are about 55 deg and the truck won't start at all. When plugged in, the water temp is about 155 deg and air intake is close to 100 deg and the truck starts right up.
Lesh - try plugging it in for a while and see if that makes a difference.