What's the 2015 GMC Sierra brake fluid type?

The 2015 GMC Sierra recommends the use of DOT 3 brake fluid, but is also perfectly capable of accepting DOT 4. However, under normal usage, it should never be able to reap the additional benefits of DOT 4, which primarily include a higher boiling point; therefore, You'll be paying a premium for an "upgraded" fluid for no practical reason whatsoever, thereby losing Your hard earned money. I only note the compatibility with DOT 4 because if You have some DOT 4 handy, it will work in a pinch. However, it's best to not mixBrake fluid types, so You should stay with what was added during Your last brake fluid flush; this was, very likely, DOT 3.