Did real incomes drop significantly since the 1950s? From what I heard, in 1950s America, you didn't have to go to college to support a large family and a stay-at-home wife. People could buy houses easily, drove giant cars and didn't worry about gas prices.

Did real incomes drop significantly since then? What was the cause?
(My college history professor had this pet theory that America gobbled up almost all the world's gold reserves during WW2, and that was what caused its post-war economic boom. Not sure if that is true, but perhaps this effect went away?)
Most of the US real earnings data which  go only as far as mid 60s. According to the statista data presented in this article by world economic forum the evolution of real hourly earnings in the US for production and non-supervisory workers looked like this:

If we extrapolate to 50s then the real earnings are now higher overall. However, this being said the real wages first peaked in the 70s at $\\\$23.24$ then fallen to about $\\\$20$ and recently in 2019 they finally again reached the previous peak from the 70s. Hence, we cannot really say they dropped significantly but rather they tended to stagnate.
There is no single agreed upon explanation for this. Some authors argue this is due to technological change and decline in demand for low skill workers (see Fernandez 2001), other arguments include declining union membership (see David,  Katz, and Kearney. 2006),  or international competition (see here). Others argue that CPI overstates inflation and that this can be also due to increase in non-monetary benefits such as health insurance (see here).  A good explainer is also provided by this brookings article.