2960tons + 4 GP7s (1500hp*4=6000hp) and with mass of the locomotive 106 tons (this is 26,5 ton on a one axle). On the 0%-0,2% track grade this is easy for acceleration, but if using 4 GP7 and take 6800 tons, you'll see differences between both results.
In any case, DDC mode not to showing real result, because config use only 3 tags from engine spec, as well Engeneer mode take from spec all tags, their more then 30 psc.
1000-1500 tons with 1 GP7 is okay, on the 0 grade.