M4/T26 forward and reverse speeds too high?

Currently the M4/T26 has the same top speeds as the M4A3 (76), both forwards and in reverse, at 42 and 5.4 km/h respectively.

Since it is a modified M4 (105), it is equipped with the R-975-C4 engine with a maximum of 2400 RPM, instead of the M4A3’s Ford GAA with 2600 maximum RPM.

I was under the impression that, due to the engine’s maximum RPM and the fact that, to my knowledge, the transmission wasn’t changed, the top speeds should match those of the M4A1, M4 and M4A1 (76), at 38 and 4.9 km/h, forwards and reverse respectively. From what I can tell, in-game it specifically has a transmission with slightly lower combined gear ratios specifically so that it reaches the M4A3 speeds instead of the M4/M4A1 speeds.
Is there any real life reason for this difference or is it just a mistake by Gaijin?