I have an '87 Pickup 22R with a 34/34 weber carb. I got a new gas cap about a month ago and I started getting what seems like vapor lock. The car stutters and jerks, mostly on the highway, but also other times at speeds around 35mph+. Once it starts stuttering, I can let go of the gas and it smooths out, but as soon as I hit the gas again it jerks like it's sucking air.

I can pull off the gas cap, and it seems to run perfectly. Is this a normal symptom of vapor lock, or should I be looking for another problem? I'm worried my carb might be the issue, but I'm not sure how to troubleshoot that.

I replaced a leaking fuel pump (mechanical) a couple months ago, and the fuel filter about a year ago. My carb is about a year and a half old -- my dad helped me install it, but I wouldn't say I know a whole lot about them.