As I recall, albeit with a memory in steep decline, others here have changed the cap to a different pressure rating than the original. But then, is your current one original? Maybe the service techs up the road at BCS have dealt with similar symptoms, but I’ve had good results with Peterson CAT, and they are more engine/chassis-oriented.
If you herein search “Surge tank cap”, there are several discussions that may offer insight, but use the “Search” tab on the menu bar, not the Search field upper right.
Joel