With my 35s and stock gearing right now, going into 4th (overdrive) is all but totally useless. I cannot maintain speed, even going downhill, on the interstate if I let it upshift. I noticed last week when I was in CA at low elevation (~3000ft) that the truck would do better but still not great. All I do at interstate speeds is turn OD off. Granted, I can do 80mph at about 3200rpm and 70rpm around 2800rpm, but if there's a hill with any real grade to it then I usually end up manually dropping it into 2nd. If it's on the interstate I'll drop it into 2nd and set the rpms around 4000, maybe lower if it's a really long hill. Point being I've had no issues whatsoever with the engined revved way out and for extended periods. I just drove back from KOH, from CA to essentially the corner of WY, and I would be surprised if there was 30 minutes out of my entire 22 hours driving there and back that were under 3000rpm.
Hope this helps instill some confidence, from what I've read our engines are way overbuilt. I'm sure high rpm will kill off some life, but so do lots of other factors so whatever. The engine didn't skip a beat so I'm not worried.