They are right, at this point it may be trial and error. Start with the cheapest part and hope it works. Or just shotgun the entire EGR system. It is over ten years old and you are going to have to throw some money at it sooner or later. Save the labor costs and replace the parts yourself.
Of course I wouldn't do any of this without further analysis, makes sense. Autozone has some decent online repair and troubleshooting info. I'll send the link that goes to the Toyota Truck section specific to EGR, but you may want to back up and look at other sections.
http://tinyurl.com/n7e5j