Battery/electrical issue

Hello, I'm been having several electrical/battery issues and am at a loss as to what to do next. Here's the chain of events:
- Truck started idling rough at stop lights. Took to local mechanic. He replaced PVC valve, fuel filter and spark plugs. Idling issue resolved.
- Alternator went out two days later. Replaced that myself. Car drove fine the next day on a 2 hour drive, however, the battery light kept coming on and off while driving.
- Truck loses all power and breaks down on the side of the road. Went back several hours later and battery had recharged. I was able to get it home just as the battery was dying and the dash was going dark.
- Took battery to be tested. Passed all testing, however they did say it was in it's last quarter of life (?)
- Found the metal connection of the positive battery cable was cracked/damaged at the terminal connection, likely when I was replacing the alternator. Bought a battery cable repair kit, replacing the terminal connection.
- Car appears to run okay, but I haven't tested it for a long duration (trying not to get stranded a third time)
- The battery light keeps coming on and off. When the truck is driving, battery light only comes on randomly, mostly when slowed down. The battery light stays on when idling.

To summarize: new alternator, new battery cable, battery passed testing. Battery light staying on when idling and randomly coming on/off when driving.

Please help!