This article contains text from the Wikipedia article on Trans-Amazonian Highway.
The Trans-Amazonian Highway (official designation BR-230, official name Rodovia Transamazônica), was introduced on September 27, 1972. It is 4,000 km long, making it the third longest highway in Brazil. It runs through seven Brazilian states, from the proximities of Saboeiro up until the town of Lábrea.
The transamazonian is crazy. You will be using it at some point if you are coming from Venezuela to populated Bazil or vice-versa. As you can see from the figure, not a lot of it is paved. The unpaved majority can be really slow considering the massive potholes and puddles. Trucks often get stuck in the mud or break down. Parts of the route have very little traffic, sometimes with only local farmers on motorcycles. So expect it to take a long time.
You will encounter a lot of dirt and mud so bring supplies and spare clothes. You should have flip flops (nobody wants your muddy feet in their truck, you barefooted hippie!) Be sure to ditch your flip flops on the top step when getting in the truck; this is trucker custom.
Only listing the mostly unpaved portions. East and south of Marabá there is plenty of infrastructure.