I recently installed rebuilt motor into 95 4x4 pickup 22re with rv cam. I have been driving for about a year and have been dealing with power issue. Truck idles fine, runs o.k, but lacks power. Going up hill I lose rpm truck only goes 75 with pedal to floor. The truck feels like it wants to go but is bieng held back. Checked head and cam, removed cat, added header, of course replaced all tune up parts. After I installed header I got o2 fault and engine check came on. I have advanced timing retarded timing gone through the head and nothing has changed. Looking in the direction of mass air sensor or o2 sensor. I've spent alot of money not to have truck driving at full potential. Problems started after engine swap. Please Help!!!!