94 lightning lacking power
 

hey i got 94 lightning with 61,00 mile and ever since i had the truck it won't hold a steady rpm if you hold the throttle it bounces around. say you hold it at 1500 rpm it go 1300-1700 won't hold steady and when you get on it try to get up but lack power until high rpms.. its mind botttlingit been complete tune up and the timing was even checked..hows a good way to check injectors and could one plugged not work injector cause this