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Joshua,Are you running a performance chip?
Code P0603 will only be set under a couple of conditions, 1) dead or disconnected battery(s) or 2) the installation of a performance enhancing program or 'chip'. Is this the only code your getting .
If you sure there is no chip and the batteries are in good shape and have not lost the connection then yes its very likely the problem is internal to the PCM. If you had the batteries unhooked then this code can set. What are the glow plug codes your getting?
The common cause for the code P0308 to set is not usually a glow plug issue but instead a failing injector on #8 cylinder or you have melted valve cover gasket where the wiring come through and that can cause a hard start as well as a rough idle.
Yes that is likely, I would start first with making sure you have good compression on #8 and if so then its likely a failing injector. See the steps in the link below to check this.https://dl.dropboxusercontent.com/u/104923897/P0308%20Nov%202.pdf