1994 chevy 2500 TBI fuel injected 350...idles great, runs good, but.........when taking off from a stop or driving down the highway I push down on the accelerator to go up a hill, I get a quick little boost of power but then it boggs and stays at the same speed. I have to push the acceleator half way to the floor to gain any speed.I checked fuel press. I checked TPS sensor. I checked timing.I replaced MAP sensor.I replaced distributor with a used one dont know if there was anything wrong with it.I checked fuel injector screens at the base of the fuel injectors.It just acts like its not getting fuel or fuel injectors are opening up and then closing back up. Or timing not right.Just dont know????????