As a "Thank You" for 10 years and 321K of trouble free service, I replaced the tired Splits with some Stage I injectors.

I pull the glow plugs, crank the motor, and get this:

<iframe width="420" height="315" src="http://www.youtube.com/embed/uHf4HR4ukNo" frameborder="0" allowfullscreen></iframe>

I go over all the usual suspects:

-Made sure the wiring harness is connected
-Charged the batteries hours before at Autozone (verified good)
-replaced starter (obviously burnt the other one up)
-replaced batteries
-checked fuses
-made sure connections were tight
-pulled DP-Tuner, same result
-RPMs register on the tach
-truck is building oil pressure and has fuel going to the injectors

What is stopping my truck from starting?

 

It sounds like you forgot to put the glow plugs back in! Go ahead and slap me if I'm wrong but that what it sounds like!
Jim & fat Monty