To Gress is a term used in the Dirty South that means to be under the effects of Ecstasy (MDMA). aka "Gressors", "Gress pills".
"Dawg Im so gressed I feel so good"
"Hey cuz you know where any gression is at?"
"You know where to get some gression"
"Ced while your in the trap I need some gressors"