'92 Sonoma won't start

K, I've had this truck for about four months. Found sometimes the initial turn-over during starting was slow, but usually fired. Sometimes it took a couple tries before it would turn over and gave that poor connection clunk. One day it wouldn't fire and gave that almost spark like sound you'd get from a poor connection or weak battery. The connections on battery had been cleaned prior. I put another battery in that I had, knowing it was a good one. No problem for a couple weeks. For the last couple weaks it started the hard initial turn-over again. I believe the hard start was not dependant on hot or cold engine and was very sporadic. Today it woudn't start and I played with connections and tapped solonoid and it started. Went to my destination and it would not restart even after tapping and playing with connections. Still lots of power to the lights under these conditions so I figured it had to be solonoid. I went and picked up a new starter/solonoid and cleaned all the connections really good and still no starter engagement.
Prior to changing the battery, if it woudn't start, often my radio memory was erased.
Today I noticed that there was no lack of power to interior or headlights but there was nothing at the starter when I turned the key.
It is a '92 4.3L with 174 000 km.

What possibilities are left and how do I test? I was thinking ignition switch but I've never had the pleasure of tearing apart a steering column and wonder if there is a way to test before I tackle such a thing.

Please help!!!

Finally took it in. It was a faulty imobilizer..!!!???