Propaganda: "information, especially of a biased or misleading nature, used to promote or publicize a particular political cause or point of view."
Gaslighting: "manipulate (someone) by psychological means into questioning their own sanity."
Propaganda, to me, is not exclusively political. It would also include advertisement. My wife taught a unit's worth of propaganda in her reading classes, as a way of increasing comprehension of reading materials. When we would be watching advertisements on TV, I'd ask her "what specific propaganda technique is being used here?" Gaslighting would be more to the point I'm making being that people are told something would be happening, and are supposed to react as if something is happening, when in fact, measurably, nothing has changed. Propaganda would cover advertisement, gaslighting would be a review were we are told that wire "X" will alter the sound when measurements indicate that the wire that costs $10,000 does not measure any different than a wire that costs $20 and there's no rational reason why the sound would be any different. When one is being gaslit, one's perception is being actively undermined. Propaganda also includes various forms of gaslighting, but the point of propaganda is some sort of special pleading. Gaslighting involves undermining the perception of others. The two are not exclusive of each other, a venn diagram would show areas of overlap. Personally, I have fallen into the trap being gaslit many times, expectation bias told me to expect a difference, I "heard" a difference. But, in most cases, a DBT would indicate no difference, particularly as regards wire/interconnects.