Just curious if the trucks computer does anything to the way it runs when the check engine light comes on, specifically if it comes on because of injector problems. Does it run the truck in some sort of safety mode? Just wondered if that is why my truck won't rev past 2000rpm or go over 40 mph since I am having injector problems (I think) or if it is just not capable of doing that with bad injectors.

You will need the codes, but it sounds more like you've limped the tranny.