Try out this addon:
http://www.wowinterface.com/download...2-SyLevel.html
BTW you are doing it wrong "Level 90+ items are WoD, which can be sold at the vendor because there gold value is higher then the dust is worth. Many of the pre lvl 90 iems have a higher disenchant value then sell value at the vendor. I suggest using Aktion Master to find out.