It appears the DC-6 Profile data was used from the tables provided (by PMDG?); however it appears that the data was not converted from TAS per Statute miles per hour (as in the orrignal tables) to nautical miles per hour (within SIMBRIEF). The result is a significant error in TAS (and FUEL) that is incorrect for the aircraft to attain for each cruise profile available.
I would be happy to submit the tables of corrections if allowed.