Trying to diagnose this new to me mighty max, been threw a few people who couldn't get it to run when I acquired it for free , I've replaced the IAC on the throttle body and had the ecm rebuilt and installed a new mpi relay just below the ecm. Truck will start without hesitation, idle up for a couple seconds then die off. Any thoughts on where to focus my time? Thanks in advance! Truck ran fine before original ecm fried. Been sitting for a couple years.