'91 Suburban, 350 TBI, 4x4, 1500. I've been having a problem with some hesitation on the highway, only at 70+, despite a new cap, rotor, plugs, wires, fuel and air filter. I'm also having a problem with my truck dying like it's out of gas, when there's still a significant amount in the tank, primarily when it's really cold out. Yesterday it died repeatedly with 1/8 tank before it warmed up enough to get me to the gas station. This all leads me to suspect a fuel problem. But I also noticed that my fuel cap says "vacuum only" on it, and when i opened it yesterday, there was a lot of vacuum (0 out, 51 a few days earlier). Is this normal? So, my question, is my fuel pump dying, or do i have the wrong gas cap on my truck?