I would imagine so.
25A * 3 = 75A. That is a lot of amps.
75A * 13.1V = 982W
982 W = 1.3 hp
Alternators are around 50% efficient, so those heaters on full blast suck up around 2.6 horsepower. That is significant. Cruising at 50 mph probably only takes 10hp.