from the first problem you discribed i dont see it being the idm but its hard to tell with out seeing the truck. the idm is on drivers side fender lookes like a pcm. the only thing it does is control inj. and if bad will definitly cause it not to start. i had a cupple of them go bad on mine due to a bad engine harness which could be you problem also. but every time mine went bad it only ran on 4cyl or not at all. it sound to me like a bad icp or ipr which controls fuel icp is on drivers side head small 3 term sensor and if i had to guess the problem i would say ipr which is the small sensor on the bottom of the hpop which controll the oil pressue to run the inj. i need around 500 psi just to start shoul reach around 2500 psi at wot. very easy to check if you have a scaner if not then just replace it and see what happens its not to bad to do outher wise disconnect oil line from head and put on gage and see what oil psi is if not 500 or more it wont start and dont forget that it can reach 2500 so have a high pressure gage. hope that helps or narrows it down at least