My first thought is a plugged catalytic converter. However, if you mean the same thing as I would when you say "lugs", this would occur any time you press down hard on the throttle. You don't mention any kind of misfire or check engine light and those would be critical clues.
Subaru Outback was created in 1995.
The Subaru Outback is sold in the US.
The 2013 Subaru Outback has 16 valves.
The 2002 Subaru Outback has 16 valves.
The 2001 Subaru Outback has 16 valves.
The 2012 Subaru Outback has 16 valves.
The 2011 Subaru Outback has 16 valves.
The 2005 Subaru Outback has 16 valves.
The 2007 Subaru Outback has 16 valves.
The 2004 Subaru Outback has 16 valves.
The 2009 Subaru Outback has 16 valves.
The 2006 Subaru Outback has 16 valves.