DerbyDad03 wrote:
I wish I had thought to do a smoke test when all I had were the gable
vents and box vents. That might have given me a baseline for what the
gables were doing.

The most surprising part of last night's tests was that the gables
were sucking out, not in. I guess I expected that the ridge vent,
which is at the highest point, would take precedence and be the only
out bound opening, with everything else being intake.

That certainly wasn't what was happening.

The gables are high, so if there's any heat source and no wind (or the correct
wind) they will naturally tend to flow out. The problem is that they provide an
easy way for air to get in to flow out the ridge vent. This will reduce the flow
from the soffits to the ridge, which works better to carry away the heat of the
sun baked roof. I imagine it also disturbs the air flow, spreading the heat
around the attic, rather than letting it flow smoothly from soffit to ridge and
out.