Is this a cam problem?

Even a stock slant engine acts kind of like that. You feel a surge of torque ~1500 rpm as the long runners give their "tuned port" effect. It is like the natural frequency of an organ pipe, and increases cylinder pressure. Mopar made an early 60's V-8 drag setup with super long runners for the same effect. Ditto, the Aussie slant intake. The variable intakes on newer upscale cars is similar, and even better, since they vary the runner lengths w/ rpm.