Jeep Battery Issues Clicking Wouldn't Stop

I have a 2000 Jeep Grand Cherokee (115,000) and a 15 month old battery that failed. Gauges read fine, but when I tried to start car when key turned, it was clicking. I turned key off, it kept clicking. I took key out of ignition and it continued to click for about 15+ minutes. During this time I stuck key back in and turned key on (all while still clicking) and my needles on gauges were going crazy back and forth. When I turned the key as if to start, the needles on the gauges went BEYOND their normal scope. Almost a Linda Blair effect. Battery was replaced, alternator check was good and it started up perfectly and immediately. Now, a few days later, it labors a bit before starting. How do I diagnose and electrical problem? Or does anyone have any suggestions? By the way, the gauges all the while read straight up and down normal.

Hey there, I had a similar issue with a 96 with a 4.0L inline 6. I replaced the starter and solenoid and now it starts up strong.