HI: Guys, I have a 2000 GMC 3500 automatic 4x4 mason dump with 60k miles, new lift pump, new injectors, new glow plugs, relocated PMD, new fuel filter, new rubber fuel lines to injector pump, injection pump timing is -75. no smoke. it seems to run good but has no power. Going up a hill it's hard to make 50mph empty. The trans shifts up through all the gears, but doesn't seem to want to kick down when flooring it, It does shift down when I come to a stop and start off again, It starts right up and runs smooth, throttles up no issue in park. I was wondering if the optical sensor could cause the trans not to kick down or some other sensor. Seems like it should kick down to a lower gear to me? Any help would be appreciated Thanks Mike