I just had a discussion with a buddy about this exact thing. We both have TTs around 8500#. I have a new 6.4 Hemi and he has an 09 2500 Chevy with the 6.0. Driving up the mountain pass he remarked he could barely hold 45 and I zipped up at 60+ and could have done more.
When he told me he (and his wife) thought they were damaging the truck when the RPMs got over about 3500 it all made sense.
Gas engines are loud which may be an annoyance but they are absolutely made to run right up to the redline regularly. As someone else mentioned keep an eye on the engine/tranny temps but otherwise hammer it.