Lower end would usually be oil control rings. Upper end would be valve seals (it's upper end - on this motor? even if your lower end is also having some blow-by the top end needs attention I'm sure).

It's also possible you're blowing too much crank gas into the intake - that happens on my volvo from time to time. Can't remember is the 3.0 is prone to the same issue.

Change your oil hot and often.
07 Taco V6 4WD 5-Auto