Really bogging down in 3rd gear

If not a Holley, and an early A, most likely a Carter BBS carb (why not tell us all that?). Good, since Holley 1920's are notorious for plugged idle circuits -> lean idle. Still, sounds like a lean idle, but verify. Close the choke by hand while idling and see if the engine likes that. If so, search for a broken vacuum hose (can often hear it, start plugging them off) or a leaking intake.