Was GRIPS the first comic at the time pushing the violence envelope? I don't think so. Maybe the most popular one to do it though. There was an endless supply of homebrew comics at the time and the more obscure they got, the more violent and smutty they got. I think Silverwolf came around towards the end of the B&W boom, around 86 or later. They say the "boom" started after TMNT #1 hit the stands, but there were plenty of B&W indies out at that time and before, just not fetching crazy prices.
The earliest I can recall off hand is the flaming carrot in Visions #1. The Carrot
would be running around with pistols in hand just blasting people on a whim.
This would be 1978.
But I am sure there are some indy zines or what not that are even earlier as the
above poster mentioned. Grips was very late to the game but rather graphic to
say the least.