FYI, you can find V fares that are cheaper but they only allow one stopover in the USA. Years ago even the cheapest fares allowed for dual stopovers.
Also, I've found that you typically need to go in/out of the same region. You can mix German airports. Or sometimes BRU and AMS, for example. Also, depending on your European origin you might be able to go in one South American destination and out from another.
Regarding D1 pricing, I got a mixed Z/T fare for $1600 and used a GUC to upgrade the return. The routing I purchased would have been over $2600 all in Z.