I have an Epiphone G-400

It has a very long neck is the neck is VERY VERY Sensitive.

If I even push the neck a TINY bit, and I mean just my grip on the neck of the guitar, it will change tune, and when I release my grip on the neck, It will go back to normal

Do I need to do a simple truss rod adjustment?

Thanks

Anyone????

Yea, any of the SG's are extra sensitive to tension because the amount of leverage created by the neck extended from the body ratio. A proper set up for your string gauge would be most appropriate. In my humble opinion, if you're playing anything other that overdriven/distored rock or < saturated sounding music with this type of guitar, buy a new one. These guitars are renowned for intonation and set up problems due to the fact they were designed by a midget.