I purchased Oreily's $22 promaster belt wondering if I have issue. Belt seemed tighter not as flexible seemed to run fine but now belt tensioner is jumping around at idle. ALT is pretty much new, one ebay $214 china units maybe 7000 miles.

I don't know anything about that O'Reilly belt but I suspect if it fit it's ok, nothing wrong with tight. FYI specs on the Gates K061130, which is a good belt, are Effective Length (in) 113.05; Number of Ribs 6; Outside Circumference (in) 113.62; and Top Width (in) .807. Unfortunately I strongly suspect that cheap Chinese piece of XXX you got off eBay has a bad alternator clutch pulley, at least that's the normal cause for a dancing serp belt tensioner although I suppose the same behaviour could be caused by a similarly bad clutch pulley on the AC compressor or viscous heater.

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Sold to LOST member my 05 Ltd, GDE Stg II turbo + TCM tune, SunCoast TC w. Transgo kit, Steiger window regulators, Samcos, Fumoto valve, 2nd gen filter head with Lub. Spec. bleeder, Hayden clutch & 11 blade fan, inverted spare, P-1 battery, BF Goodrich Long Trail TAs, Etecno1 glow plugs, timing belt at 50K miles/8 yrs

What kind of pulley is on the alternator? Can you post a pic or read a brand name off it?

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05CRD: GDE Hot ECU & TCM tunes, Provent, Cat filter, Facet lift pump, TransGo kit, Florida TC, Samcos, stainless brake lines, HDS thermostat, Renegade light bar,
RL super sliders, Bilstein adjustables, Al's Gen 4.5 Arms, 235/85-16 Duratracs, DTT rear, Elocker front, EVIC+TPMS, Turbo timer, McNally pillar gauges, Weeks Stage II kit.

Here is alternator

http://www.ebay.com/itm/ALTERNATOR-05-0 ... 33&vxp=mtr

Pull the plastic cap off of the pulley. does it say anything underneath it?

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No nothing underneath it, does have killer looking torque screw though.