c-4 won't shift out of first, hooked up modulator valve, but don't know where it goes to engine

The modulator only affects the QUALITY & TIMING of a shift, but mostly does this by either raising the line pressure at low vacuum, and lowers it at high vacuum. You MAY be starting out in 2nd gear and with extremely low line pressure from little or no vacuum signal and you can damage whatever clutch pack is trying to apply and hold against very low apply pressure. Starting in Drive, the unit receives a command via the governor to start out in Low (low/reverse clutches applied and 1st gear clutch with its reduction sun gear set activated). Soooooo.... if you aren't feeling the unit dropping into Low, especially if you rock back and forth from Low to Reverse, I'd test the line pressure since there should be a distinct change in feel if you perform that test. At any rate, find a manifold vaccum tap that is NOT modulated by the throttle position eg: ported by the tip-off or throttle opening secondary or tertiary vacuum supply ports, as any of those will shortly kill the trans clutches when they receive the wrong information about the true manifold vacuum value. BTW: a "governor shift" as mentioned above would be disastrous if you did it a few times. The governor won't bump the line pressure by much, if at all unless there's a working, correct vacuum supply. The governor only "talks" to the valve body and is effectual mostly in downshifting for a stop, on this unit. To dispel an olde wyves tale: Clutches and or bands do not slip, as most people assume, during a shift. If one had a direct connex with the engine to the input shaft of an automatic transmission and it were to shift, the hit would quickly confirm that the torque converter was the object that makes a shift feel softer, smoother and less tooth jarring. The clutches will die very quickly if any actual friction element actually slips.