when ever i go past 4000 rpms my truck stops pulling. every gear is like this. could it be from not having enough fuel? i have a 255 walbro and i am running 8 psi now. i have a safc 2 and have it somewhat tuned. i messed around with the safc 2 but there was no difference in performance. all i could feel was that the truck wouldn't run as smooth at some points. so i just put everything back to stock settings.