Idiots...

I wouldn't flame the shop. You are lucky to have found one that will even touch a carburetor. Modern fuel injection is much easier to trouble-shoot. You can separately verify fuel pressure on the rail, that injectors are commanded to fire, and even remove injectors and flow test them, or just replace them. That all takes money, but they rarely have problems. Nobody can tell you what is going on inside a carburetor, and trouble-shooting is just a series of guesses and taking it apart to see if everything looks right.

I am guessing this was the 1970 Dart 225. I had a 69 Dart slant for 20 yrs. If you have the Holley 1920, it has a sealed innards assembly, which nobody can look at and know it is OK. I went thru at least 3 of those carbs, with crappy idling and dying at red lights for years until I found one that made it purr like a kitten. Also, your "oil light comes on, then goes away" is common. I think it is usually crud against the oil pickup screen. Since it is hard to pull the oil pan, try draining the oil and filling the bottom of the pan with gas or kerosene and let it sit for a week. That might dissolve the gunk.