Could use some help??

[Bad Dog]

I have a question about my truck, and I was hoping someone could point me in the right direction.

I own a 1970 c-10 with a 307 c.i. v8 and automatic. My question deserves some history first. About 6 mos ago, I went out to the truck and turned the ignition key and for the first time I got NOTHING in response. As most of us already know, this could be the start of something bad. I proceeded to do absolutely nothing in terms of fixing the truck because from that point on if I just turned the key enough the solenoid would engage and the truck would turn over. Each time I did this though it took longer. I just figured it was the starter / solenoid so I'll unhook the battery, then the ground on the starter, then the power wire with the two mounting bolts and replace the whole unit at once and its fixed right.....NO ! I went to the local AutoZone for a test of my second rebuilt starter and it was not passing their tests. I picked up the ' deluxe ' rebuilt AGAIN and reversed everything I mentioned earlier with the battery cable going on last. I went into the cab and damn it if the problem had not changed at all. I have checked every wire I can see, and since the truck has NO options at all, its pretty basic. Hell, it it was a six banger with a stick shift then it would have NONE of what was offered by chevy at that time. so my question is, what would stop the starter from doing its job??