81 d150, 318, comp cam, eddy intake hei ignition, electric fuel pump, 354 gears.. Truck idles great but it stumbles a bit if given gas. My timing is dead on an checked an rechecked 50 times. It don't back fire, just stumbles/has a flat spot when gassed. Any pointers?? Has the 6.5 power valve stock #28 or #31 sprayer, 65 jets.