Batteries

You can't just stand there and wish it's fixed

Some of "whut:"

1....I noticed you mention trunk.........so cable connections, size, and GROUND from trunk to engine

2....Starter could be dragging when hot a common problem esp with the older wound field units

3.....It's possible you have an engine problem, rod, main bearing

4....Yes, both batteries might be getting weak/ old. Have it / them load tested

"Rig" a long piece of light gauge wire with alligator clips, long enough to reach from front to rear. Spend part of a day when you can mess with this. Warm it up and see if you can duplicate the problem, but in any case get the engine FULLY warm

Clip one end of the wire to the NEG battery post in the trunk. Run the wire up front, hook to your meter. Hook the other meter lead to the engine block

Crank the engine, note the reading, and crank it and read AGAIN with coil wire unhooked / grounded

You are looking here for a very low reading and you don't want more than say, .2V, that is 2/10 of one volt

Now do the same thing on the positive side............Hook the alligator to the POS battery post, come up front, crawl under, and hook to the big starter post. Again crank, and with coil wire grounded. Again, you don't want a high reading the lower the better, not more than 2.--.3V max

Now, leave the meter on the starter post, and move the other test lead to the engine block. You should read battery voltage. Again crank the engine. You want the "higher the better" 10.5V is about min, I would not accept less than 10V.