*After the update on November 3, 2015, it appears you only need to upgrade the first 4 trucks in the game instead of 6 (The New York levels were not supposed to be in the initial release of the game). While I cannot confirm this myself (I unlocked this pre-update), that is what I have seen others say. This makes this achievement much easier to obtain.**Thanks to dieotze74 for confirming this unlocks after level 18 of the New York chapter*
*I can also confirm that this is true. New York level 18 has the last unlock. Be warned that the last 2 upgrades cost $18,000 and $25,000 respectively so 3-starring all levels is important to have enough money*
Once you accumulate enough money, the game will prompt you before a mission to upgrade your truck. There are a total of 6 trucks in the game to upgrade. Each truck has 2 upgrades. You should have enough money for upgrades if you are 3-starring each level.
Once you fully upgrade your first truck, you will also get the following achievement: