poor running 16 Valve

89 16 vlv recently replace head due to broken timing belt. It idles good, but won't rev over 1,300 rpm. rplaced plugs, triple checked timing, replaced mass flow sensor, fuel pump, FPR, and filter but still won't rev over 1,300 rpm. The shop checked the head and says it good. Any clues as to make it run better?

TIA !!!