2004 5.9 6 speed,Walbro fuel system set at 20 psi, AFE cold air with ram air hood: surges at 2000-2200 rpm no matter which gear (4th, 5th, 6th). No error codes, fuel pressure is steady. Had #6 injector changed due to mechanic saying it was 103% and all others were 97-99%. Rail pressure checked OK. Under acceleration every thing is good. No surge under decel.
Any suggestions?

 

Turned out to be 4 of the other injectors all letting go at the same time.