Replace those glow plugs like yesterday before tips fall off and cause engine damage as has happened. Yes in warm weather the vehicle will start just fine with glow plugs not working.
As to the P0299 see my comments as to one possible cause at
viewtopic.php?f=5&t=77010&p=808355&hilit=+p0299#p808355On the other codes go to Sir Sam's NOOB guide and follow the links to download a copy of the 05 and 06 FSMs (05 lacks diesel cooling data and diagnostics but has illustration keys while 06 is the reverse). Look up codes in 06 manual for hints as to issue.
If she lacks GDE tune then get one but only after glow plugs get done IMMEDIATELY