1997 Silverado Starting Problems

I have a 97 5.0 L auto truck, the problem begin with going out to start truck and it would turn over but would never start. You may go out in a couple of days and it would start right up. Next time out might not start. This went our for a couple of months. You never new if the truck was going to start or not. It finally quit doing that but now the starting problem is this. The truck would start fine first thing, then if you stop somewhere and then start the truck it turns over very slowly. Sometime it didn't turnover at all and kept the key switch held in the starting postion and it would decide to start. I had the battery load checked and it was ok. Finally seen the voltage gauge drop one day so I put on a new alternator. Still doing the same thing, went out to start truck and nothing happen when I turned the switch on and turned in on again and it started. Now it is back to the slow turning over again. What to check now. I have put a charger on the battery and for a few days it starts right up and then slowly starts the slow turning over again. Changed battery and still doing the same thing. Has the new alternator. HELP PLEASE............thanks

Geta starter draw /load test done, especially hot, confirm good grounds from the battery to the engine also.

This may sound stupid, but I had a simular problem on a older truck. I replaced everything battery,alternator and starter. I was told by a neighbor to replace the cable and I thought...that's not it, the cable conducts so why replace it. Well it turned out that a 6 inch section cable (by exhaust) would get high resistance with heat, evenually it permately created a resistance (like a piece of tungsten). The point is copper can lose it's conductive properties if exposed too much heat, too long.That problem was a pain in the ass for about a year till I finally changed cable. Furthermore I had more trouble getting it started when hot, if I had a booster or jump I could get enough electrical flow to get past the bad spot in cable to start.