I think the Challenger 2 use an older engine. The export model in the Greek trial apparently had a new German 1500 hp diesel, and IIRC both the Challenger and the LeClerc (using same engine) were noted for their good range in the tests. The M1 has 1900 liters of fuel and the Challenger 2 apparently has about 1600.
edit:The primary problem for the M1 is that it needed the turbine to produce the power needed for its electrical system. It consumes nearly 40 liters to start up and about 45 liters/hour when idling. It is also an older engine so it could easily get better if they found the money for the next generation engine.
edit2: I just checked some numbers and the M1A2 SEP has less fuel (1680 liters) and a range of just 350 Km compared to the about 450 Km of the M1A1. Compare that with about 450 Km for the Challenger 2 and maybe 550 for the Leopard 2. But it is easy to find conflicting numbers so cannot be sure.