93 Ranger extended cab, 4 cyl, over 300,000 miles, manual

So, I'm not sure what part of this story might be related to the problem, but here's all that happened up to the problem I'm having.

My tensioner pully has been squeaking a bit. So a few weeks ago I sprayed some belt conditioner on the serpentine belt and into the pully (at the suggestion of the parts store guy - worst advice ever) while at the gas station. Sounded worse than it did before when I started it up. On my way home the whole thing started to overheat, with steam and a bit of acrid smoke coming from under the hood. Once home, popped the hood, and the radiator cap was cool, so I took it off (I have been having a slow leak from the coolant system forever) and let it cool off. I filled it with water,and drove it, and everything seemed OK. A few days later I ran the tank to almost empty (waiting on paycheck to be able to fill it) which I never do, trying to refill it when it's around half to a quarter tank. The next day the problems started.
When accelerating, during the lower RPM's it stutters, or bucks, as if it's not getting enough gas. if I try to rev it, it gets a bit worse, and if I ease up on the gas then it seems to run fine. Once in higher RPM's it's fine, until I have to shift. Once in a while it will pop or back fire while pressing the gas. When I rev the engine with no clutch engaged, it doesn't have any problem. If I gun the engine, then drop it into gear, sometimes it will engage and go without any problems, but will still sometimes buck.
It tends to happen more when there is less gas in the tank, as when I filled it halfway it was fine for a day or so til it got lower. I'm hoping to fill the tank soon once I get paid to see if it goes away.

I think I had this problem a few years ago and I had to replace the cat converter, and I've read articles saying the EGR valve could be the issue, but I don't believe my truck has one. Also that it could be water in the gas.

Any suggestions as to what might be the problem, or have caused it?