Sorry for the scare Gary :(.
I've seen a few let go during a 'rev tune' on the freeway to clear the old sticky valve problem. That's probably holding the revs up around 5000-5500 for a few km so not a normal thing to do.
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occasionally I have hit 5500 and above in sand with the 4.6 she is fairly howling at that but it doesn't sound like it is about to self distruct.
Obviously not a 3.9 - when I had the 3.9 in her the highest that I took it was in mud up in the N.T. and that was about 5 - 5 1/2k, I wasn't watching the rev counter as I was trying to get unstuck and having a ball as well, again it didn't sound like it was about to self distruct but it didn't sound as free as the 4.6 either