Move from Fuelly
Export your fuel-ups from Fuelly, then import the file into Full Tank. Four steps, and the MPG check shows that the numbers match.

On fuelly.com, open a vehicle and use Export Fuel-ups. Repeat for each vehicle you want to bring over.
In Full Tank, open More, then Import from file, and choose the file you exported.
Full Tank recalculates MPG for every row and compares it with your file. The green line shows how many rows match.
Your vehicles, fill-ups and services are added. If something looks off, nothing is imported until you tap Import all.
Work Truck 42 · Family SUV 118 · Weekend Bike 14