that new I would have to say it could only be a stiff shifter boot.
2005 and 2006 Wrangler Unlimited LJ 2 doors were available in Rubicon and Sahara models...
I have had a similar problem with my 1991 Wrangler. I found if you can pull the 4X4 stick past the 4 high the push it back up it may engage. That worked for me. The problem was ultimately fixed when I had the transmission rebuilt.
You can search the Internet to download a Jeep Wrangler owner's manual for free. You can also try contacting Jeep directly for a copy of the manual.
The 2003 Jeep Wrangler has a 5-speed manual.
The 2011 Jeep Wrangler has a 6-speed manual.
The 2005 Jeep Wrangler has a 6-speed manual.
The 2010 Jeep Wrangler has a 6-speed manual.
The 2001 Jeep Wrangler has a 5-speed manual.
The 2012 Jeep Wrangler has a 6-speed manual.
The 2009 Jeep Wrangler has a 6-speed manual.
The 2008 Jeep Wrangler has a 6-speed manual.
The 2007 Jeep Wrangler has a 6-speed manual.