Here is the full list of all 19 Tumbleweed Express achievements.
Find all golden envelopes
Achieve three stars on all Badland levels
Achieve three stars on every level
Achieve three stars on all Desert levels
Use TNT to blow up at least two enemies simultaneously
Complete five contracts at the same time
Fully upgrade a freight car
Interrupt the status quo
Achieve three stars on all Cliffside levels
Acquire every Caboose Turret Type
Overcome a bitter rival
Purchase an automated turret for all freight cars
Achieve maximum train length
Defeat the leader of the Drillcar Bandits
Complete a level without losing a single freight car
Achieve a three star rating in any level
Complete a contract
Return to the Warehouse
Find a golden envelope