I never priced out the OEM Serpentine Belt Idler Pulleys, but I will be buying two pretty soon. I bought the 36101 Gates version from Amazon, and it's the same diameter, but it is made in china (the OEM one has an NTN bearing) and it does NOT roll freely. It makes maybe a 1/4 -1/2 revolution when I spin it, versus the OEM with 100k spins a few full revolutions when I spin it with less force. The Gates pulley is deeper, and has a rounded edge which allows it to only mount one direction. Luckily there is enough clearance to mount it to the engine.
here is a picture showing the face of the Gate and two OEM

Here is a picture showing the depth.

Here is it mounted

And one more with the new Gates belt also from Amazon. The belt was maybe a half inch shorter than my OEM belt (only about 30k on the OEM one, looks perfect so I will hold on to it for a spare)

I am assuming this Gates Pulley is the same as the 6101 from Napa if you decide to go that route.
*EDIT* IDparts has the pulleys for 33 bucks
http://www.idparts.com/catalog/product_info.php?products_id=2884 and I paid like 16 on Amazon, not worth saving 35 bucks for two in my book.
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05 CRD Sport Dark Kahki
RRO: Adventure Rack/Rails ** MOPAR: Skids/Renny Flares & 255/75r17 (32.1) BFG M/T on JK wheels ** ARB: Bumper/IPF lights/790/948/shocks ** GDE: TCM/Hot Tune ** ROCKLIZARD: Super Sliders/Komodo Bumper
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