RPMs at speed/shift points/should I road trip?

Thanks you for the welcome to the board re: my other post.

I was on a stretch of highway just sort of cruising and it seemed to be revving higher than I remember from the last highway drive. At 60 to 65, the tach is at 3000 RPM give or take. Is this high? It felt a little high to me, but after getting off and driving I made sure that fourth gear was cominmg into play. This is an '84 300 TD. Other than that, no probs except the speedo needle doesn't like to move now until I'm going 10 - 15 or so, then it jumps up.

I was thinking of taking a trip of about 250 miles each way for Thanksgiving but if something goes wrong I'm up a creek. I think I just answered my own question there. Well, what about the revs and as there isn't a redline on the tach, whats the story about revs and a diesel. I can't imagine long distance cruising at 3500+ RPMs. Seems harsh.