2002 and later trucks will not have a tack reading untill after cranking. If you can check the injector wires just outside on the VC during cranking they should show 115VDC if no voltage that pretty much points to the IDM.

Injector leads

G G I I C I I G G
1 2 3 4 5 6 7 8
G- Glow plug Ohm to block ground
I = Injector +
C = Injector Common -