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