Why does my second gear pop out ?
 

so I have a 2004 lancer EVO GSR 5 speed with lil over 115,000 miles on it I having issues with second gear when I down shift from 3rd to 2nd it will pop out of gear or when im in second and let off the gas quickly it will pop out. it never pops out when up shifting from 1st to 2nd even at full wot. Has anyone experienced this and can give me details on why this is happing. what can I do to fix it ? Could it be the syncro for second or do I need to get new trans. thanks in advance or any help.

It's a hub/slider issue.
There is a cut in them that hold them in place when you select a gear and when they get worn they behave like this.
Unless you have an issue where your engine is rocking too much when you back out of the gas that it tugs on a shift cable.

Thanks for the info. what can I do to fix this issue take the trans and have it rebuilt ?

Yes, after you rule out the possibility of the engine/trans rocking and pulling on a shift cable.