Truck won't turn over
 

Hi New Member here so I will try and get this right.
I have a 2007 F-350 6.0 Power stroke. About a year ago I had the heads replaced and bypassed part of the EGR my mech said it can cause your head gaskets to go. He put an SCT chip in so it ill pass Utah smog. (He has the same truck as I do) I went to start the truck the other day and it seemed as though the batteries were going and sure enough he batt light came on but then went off. Then the truck would not turn over at all the next day. I checked the batt and the were old corroded and had no charge. I replaced them tonight and the truck still will not turn over. It makes that noise of very slowly trying to turn over but I did that with the old batteries as well. I hooked up the SCT device and looked for error codes and got a P0683 Glow Plug Control Module to PCM Communication Circuit Code. Looked it up and cannot tell if that would cause the engine to not turn over or not or if I have more than one problem.
Any ideas before I plunge off the expensive tow it to the shop solution?

If the starter is on its way out it wont crank the motor fast enough to produce the required oil pressure to fire the injectors. Ive run into this on my truck.