peppper

So whenever I try to play modpacks like forever stranded, tekkit legends, attack of the b-team the game doesn't respond and is laggy, I tried searching for fixes but after 2 hours I have found nothing, but when playing something like tekkit classic, It works no problems but whenever I use a newer version It is extremely laggy, though my pc should support it since i got a gtx 960 and 8 gigs of ram. I just don't know what else to do than ask here and hope someone knows the answer.