Quote Originally Posted by nealpellecchia View Post
Ok, my 1993 6.5 has a severe suction when you take off the "new" vented gas cap.
I suspect you meant diesel cap, but it's helpful that everyone knows that there is a big difference between a fuel tank cap made for a gas powered truck versus a 6.5 diesel truck. You must specify a "diesel" fuel cap when buying a replacement.

According to GM, a diesel fuel cap should vent when internal fuel tank pressure exceeds 2-psi or 1" vaccum. Gas caps are generally not vented, which would create huge vacuum as fuel in drawn down in the tank.

Jim