A load tester is a great tool to use on an annual maintenance schedule. Place a place a date label on them as well. Check them when you lift the cables for cleaning. On the crank issue it may very well be a starter. They do wear out, and don’t go overboard with high end replacements unless you have a demanding environment. There are amperage tests for starters, you have a vintage truck, going to need good analyzing tools, and the skills to use them for the long haul. Take your time, find intelligent videos, good manuals usually have testing techniques. Haynes, not so much, but usually provides a general idea of repairs. Don’t take shortcuts, the next guy to repair it again might be you. Ive had my 91 350 for 20 years, bought it from a well drilling company. Hard life. Pushes snow, dump insert, loaded to the max and then some. Mine is called Wonder Truck. I wonder lots of things about it, start, stop, get me home? Great rigs as you all know.