It might be the IPR. It is located on the back (firewall) side of the drivers side head. You could unplug it and start the engine which will fool the computer into thinking the IPR is working correctly. Be careful, and if it sounds like it's running smooth you may have found the problem.
I think it sounds like a FICM voltage issue to me... And again it's a somewhat easy check but, you will need a 5/16 wrench/socket, #20 torx bit, digital multi-meter, and an assistant. 1st you need a cool engine, use the 5/16 and unbolt the degas bottle (coolant reservoir) finaggle it down and to the right exposing the FICM mounted on the valve cover. Be careful not to unplug the hose that goes to the manifold, it will leak coolant. After that you will have the FICM exposed. It is the aluminium thingy with a 1 inch by 1 inch black cover right under where the de-gas bottle was mounted. You could then use the #20 torx bit to remove the inspection cover. under the cover should be 4 small scews holding on 4 wires. Don't panic if there is 7 it's just an older FICM. Ok, if you are breezing though this PLEASE, pay attention here: While testing the this unit you MUST take caution to protect the poker on your multi-meter from grounding out on the side of the housing (THIS WILL CAUSE DAMAGE!) I wrap the everything but the tip with electrical tape. The screw that is nearest the drivers side fender should have 46-49 volts when the key is on. Now is when you need the assistant (unless she already got you some iceed tea) Have the assistant crank the engine with the instructions to turn it off if it does start. While it is cranking you should still have 46-48 volts. If you have less than 45 volts at any point in this process you have yourself a failed solder joint inside the unit. If you are handy with a soldering iron you can watch the youtube and do it yourself but, keep in mind that the pro's won't work on it after you open it up. If the youtube looks too challenging for you I recommend one of the professionals like Swamps that do this type of thing everyday. Plus the pro's can unlock up to 80 extra horses for you too...