Changes

Argentina has a reputation for variable to long waiting times. Several hours isn't unusual overall.

It seems to be much safer, faster, and informative to ask drivers at roadside stops such as gas stations and truckstops. Standing on the road with a thumb out can last for hours, and is really a last resort. If you want to go far, go with the truckers. They will carry you sometimes over 1000 km, and leave you at a good place to continue. Just keep asking. When you're looking for a ride at truck stops, keep an eye out for Brazilian and Chilean plates. Truckers from these neighboring countries are usually much more willing to give you a ride than the Argies, who will bullshit you about the transport company having sensors in the seats and harsh fines for taking riders.

It's considered normal to ask the people working filling tanks at gas stations to ask people for you. If you're a foreigner, do mention it! A Dutch guy mentioned that it seems to be a lot easier to get rides.