My batteries keep dying and won't recharge!

Good, that means it isn't likely to burst into flames from a short while we're talking! A fully charged group 1 should be able to run the truck for more than an hour without the chargeing system working, if you are only getting a few minutes then there is something putting a big draw on the battery or it only has a light charge on it.
It takes about 10 hr to fully charge a discharged battery, and most of the time it will be charging at only a few amps.
I run deep cycle batteries in my truck for heat and cooling at night, I only dis charge to 50% or less and it still takes 10 hr of running to re charge.
If you are charging, cranking and dis-charging and not fully re chargeing in between it is very quick ruin what was a good battery.
I would put a charger on and monitor, the battery should never get hot, (above 100 deg) but might get warm and you get some "gassing" from the cells. If possible check with a hydrometer and watch the Spf gravity of the electrolyte, and stop charging when it ceases to rise after two consecutive reading taken an hr apart.
You don't want to charge much above 20 amps with a battery of that size, slow and long is much better than fast and hot.

I know I haven't mentioned this, but there may be a problem with fuel pump, as well. When I got it running that one time it was getting fuel, but the next time I tried running it there was no fuel going through the fuel filter. Since then I replaced the online fuel filter, and I cleaned out the fuel line, but it still is not sucking in fuel, so I think I may need to buy a new fuel pump.

I am cranking, recharging and cranking without running the truck because I have to fix the fuel problem.

Could be a fuel pump, but could also be rusted fuel line with pin-holes. I'd run new fuel line before deciding about the pump, if it is getting air, it can't move fuel. Don't be tempted to use an electric "solonoid" type pump, either use the original or a electric rotary vane pump, but if you go with electric, add a rollover switch and an oil pressure switch to shut the pump off if the engine stalls or rolls in an accident. A good electric will set you back about $100.
Some fuel tanks have a "dip tube" that draws fuel from the bottom of the tank and out the top. if the dip tube rusts inside the tank, you can't draw the fuel out.
I made a "drop tank" out of a gallon can that thinner came in, with a small (5/15 or 3/8) tube brazed in the bottom. you can hang this above carb level and hook line from it to the fuel inlet on the carb to run the engine while figuring out what else is wrong.

Unless you our allowing 10 hr of charging between cranking attempts, I think that is your problem, you have a battery that is mostly discharged and only has a surface charge on it.
Put it on the battery charger at the lowest 6 volt setting, let it charge for 10 hr as long as the rate is less than 20 amps, it should taper to just a few amps within an hr and stay there for a long time.
Most battery chargers have an auto setting for 12 volt but not for 6 volt, so keep an eye on it, check the battery to see if it is getting hot.

I don't believe there is any holes in the fuel line, and I found a new mechanical fuel pump online that I was going to buy.

I may look into getting my generator rebuilt also.

I will have to talk later. I will get back to this topic then.

I may look into getting my generator rebuilt also.

Hold off on that for now. It isn't cheap and may not be the problem. Once we get the other problems worked out I can give you a couple of quick tests to see if it likely needs work or not. Most don't. I have purchased plenty of trucks, and generators an haven't got a bad one yet. My '48 is all original (got it from the original owner) and it still works fine all these years later.

Ok thank you! I may have more questions next weekend.