Bad gas? Bad plugs/wires?

When cranking up after it’s been sitting, say overnight, it sputters like it’s not firing on all plugs or wires. It will continue to do this until, although it may not be related at all, it gets warmed up/been driven for a few mins. When it’s sputtering, heavier acceleration only makes it sputter more while letting completely off the accelerator at that point, kills the sputtering. It’s only started about a week ago. Again, although it may not at all be related, it’s been running warmer than usual. I’ve flushed the radiator, noticed some leaks and bought Stop Leak. Since putting the Stop Leak in it, it’s definitely stopped most of, or nearly all of the leaks I’d seen before but the engine is still running a good bit warmer than usual. I keep a check on the reservoir but it hasn’t lost or used any water whatsoever yet every time I leave to go somewhere, I’m having to fill up the radiator itself. MOST of the time, just staying moving will keep temp at manageable temp but not all the time and the heater will also help from time to time, though not every time.