Um, 3300 at 70 seems about right. Are you sure you aren't just counting the 2 shifts from rest and assuming you aren't reaching 4th? MB transmissions start in 2nd gear unless pushed hard off the start. Use your shift lever, start in the lowest position, push it fairly hard from the start, shift manually until you are in drive and count the shifts on the way up. You may find that it's 1st gear you haven't been seeing, not 4th.
In 3rd gear on the highway, your engine would be screaming at 70