Mine's doing the same. I have a 99' with 117, XXX.
My hubby checked Spark Plugs and found to be rusted. We are now in the process of changing.(Long process with DOHC).
Anyway, the only difference I see here is that mine doesn't fluctuate with the RPM's. It just kinda feels like it's running out of gas. I've been told by one mechanic it's the tires, another says Spark Plugs, another said EGR (which I replaced and check engine light still on).I'm WAY confused!
But it Def. Sounds like we may have the same prob.