1994 Pontiac Bonneville. Head Gasket or Intake Manifold failure?

have a 1994 Pontiac Bonneville, according to everything I've
researched (VIN & Year), it would be a 1st Gen. 3800 engine. It is
smoking from the rear of the engine (or towards the firewall, rather)
as well as the tailpipe. It looks like a head gasket problem, but it
has passed two mechanics leak down tests for head gasket failure. The
smoke coming from the firewall side of the engine, materializes away
from the block, coupled with the fact that there is a lot of smoke
coming from there, I can't really tell where it is coming from, other
that relative area. The smoke is white, and it smells like coolant,
however the temperature guage doesn't budge from where it should be,
and the smoke will stop eventually after driving the vehicle around a
bit.
I've heard problems from the intake/EGR scenario in these cars, but
only on the Gen II's. Has anyone else had there upper plenum fail like
this?? And could the head
gasket still be bad even though two tests have come up negative.

If anyone has had this problem and fixed it, I would be greatful if you
could lend some advice.

Thank you,
Chris