1997 Chevy Truck Hard starting

Electrical problem
1997 Chevy Truck Two Wheel Drive Automatic 109697 miles

We have had this truck for several years I has a V-6 gas engine. It has progressively become harder to start. It sounds like it is out of time. The starter labors to turn the engine over. I had the starter repaired with a new armature as it was burt in many areas. When I installed the starter again the same problem existed. I has gotten to the point that it will rarely start and when it does the idle speed increases and decreases like a gallop. I can only assume it is an electrical component but am not sure where to start.