Welcome to LOST.
Good price on the CRD,
I can recommend GDE from personal experience. Probably the biggest benefit is minimizing the EGR.
For air, stick with the stock air box, no one has reported improved performance with any other mods.
Can't go much higher than 2 1/2 lift on a CRD without risking trashing the CV joints. 2" is safe. The CRD axles are different than the gas models. The drivers side shaft is shorter, higher means bigger angles.
On the exhaust, there is a constriction near the CAT, eliminate that and the muffler and you'll do just about all you can there.
I use power service in the winter, but don't add it on a regular basis. Not quite as cold as Duluth.
Welcome....
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2005 CRD "
Ol' Blue"
Red Ryder carbine-action, two hundred shot range model air rifle with a compass in the stock and this thing which tells time.
My build page- RL Komodo Rear and TJM Front Bumper, armored, lifted, JBA Steel D30, 4.10s and ARB air lockers.