Shouldn't be a problem. Your rpms are high because of the 4.10s in the rear...my 97 with 3.73 gears is at 2000rpm at just over 70mph. If it bothers you could always go with bigger tires to compensate.

I believe you could hold these trucks at "redline" on the tach all day long and not have a problem. My thinking is that redline on the tach is a "fuel injection limit" and not a mechanical limit of the engine. If possible I would think a powerstroke engine could spin at least 5,000 rpms without a problem...but getting the fueling for that rpm would be a problem.

An apples to oranges example is our TDI engine. It's "redline" on the tach is only 4500 rpms and won't rev beyond 5000 rpms...however...the internals are almost identical to a 2.0L vw gasser engine which redlines at almost 7000rpms.

It is a question of fueling.