I agree with the above posts by Fast and Bee1971.

I had an XE cam in my 470. I'd heard people bash the XE line for years but, was one of the lucky ones that could get one to rev past 5500rpm or so. The car pulled clean to 6200 without issue. Put a set of ported heads on my car with different springs. Picked up around 40-50cfm in head flow and the car went no faster. With the new springs, the lifters were not happy starting around 5400-5500.

I did similar to what most have tried with these cams and thought I had an issue but, it's the cam. I've never seen anything like it in the past. When people say "hit the wall" or "it's done at x rpm", it's no lie with the XE cams. My car sounded like it had a rev limiter on it, it truly would not rev past 5500-5700 rpm. Can't remember where I saw it but, there was an article I found where they dyno'd one of the XE cams and ran into similar issues. Tried a whole bunch of different things with little success. It was interesting to see the curve when the cam get's unhappy.

Called Dwayne (Fast) earlier this year and had a SFT ground.

The XE cams, for the advertised power range, really work well but, they are done when they say they're done.