All a puff of blue smoke is at start up is generally valve stem seals. Especially if thats the only time you getting it. Actually it's just the exhaust valve seals. The oil sits up there when you shut it down and seeps into the cylinder. At start up you burn that oil all at once and get the blue smoke.
My 5.0 did it, and my 22re did it until I changed the seals. I'm not sure how much of a PITA the 3.0 is to change. Maybe someone else will chime in.
Good luck,
mike

'86 4Runner 5" SAS
'97 4Runner
'05 Corolla
'00 F250 PowerStroke