white smoke

[Dave]

"More likely is that a gasket has given up somewhere and is allowing coolant to get into the combustion chambers (i.e. blown head gasket)."

I already changed the head gasket.

where do you get a compression check done? and what's a leak down test?

How come you changed the head gasket?
When you did, did you torque it down to spec? Did you re-torque it after you had a few hours of driving time on the new gasket? If not, your new gasket could be the failure.
As DJ said, a compression and leakdown test will give you a bit more info on what's going on.