Can't say I know the JP/Viper in depth, or at all (although we did use it for training during my time at RAF Halton sootie school 30 years ago....ahem!) so not sure if Viper has this kind of arrangement.....but generically, my first thought was intake pressue sensing (P1/P0) either leaking or semi-blocked giving inaccurate pressure signal to a fuel control unit, or jet pipe pressure (P7 in RR Conway terms) limiting fuel flow. HP Fuel Pump and Fuel Control Unit governors adjusted correctly? EGT normal so not temp limiting? Anti-ice/bleed valve not fully closed?
Long time since I worked on non-FADEC engine also!