When you changed the computer, did you transfer the old ROM chip to the new one? The ROM is specific to the equipment on your truck. The same computer may be used on different models. Could be something like a bad crankshaft position sensor saying the engine isn't turning. You may not fix this one without connecting it to a computer and getting the readouts of all the sensors.
Two things you can do, at
www.factorymanuals.com you may be able to pick up a real shop manual for what you would pay for a less useful book at an auto store. I don't feel right about using this site to send you to another. However, we lack good automotive people here. Try
http://theoildrop.server101.com/cgi/...?ubb=get_daily