The early throttle-body injection control systems were imitative of the more advanced carburetion systems of the time. Is the hi-idle low-idle kickdown functioning properly? This may be malfunctioning due to a bad vacuum diaphragm at the side of the throttle body
as for the electrical problem, did you purchase the vehicle like this? There's a possibility they maybe connected.
Go with the simple stuff first, check all your fuses. Then make sure your alternator is giving you the proper output. Sounds to me like possibly somebody did a poor job of reassembling your top end.

 

I buy the truck and put a rebuild motor in it

 

Maybe you are just going faster than the speed of light?[8D]

There are two possible causes to your problem, thinking in general terms here.

#1 something is demanding more electricity to help speed up the car. The only thing I can think of is the TBI injectors. They don't need that kind of power. So the only way they can be the guilty party is that they have a bad connection that gives higher resistance as power demand goes up. Check fuse, wires and connections associated with the injectors.

#2 something completely different is falsely leading power to ground. With low rev's on the engine the resitance is to high to allow a noticeabble current to pass. But when you speed up the power becomes strong enough to overcome the resitance and you loose power this way. The fault can be almost anywhere, but lampsockets, stereo or other electric components are likely suspects.

Warning! Both of these conditions will lead to increased heat locally and be a potential risk for fire! Get it fixed!