It sounds like the load that you are placing on the engine would be considered acceptable. The issue of whether you are lugging the engine (prop pitch/ gearing) is still unanswered.
As suggested by k1vsk, the first thing to do is to verify that your tach reads properly. Next, you need to make sure that you can actually hit your maximum rpm while in gear, not just in neutral. If you cannot, this means that you are putting too great of a load on the engine. This load could be due to marine growth on your hull and or propeller (check this first) or due to improper gearing or propeller pitch. If you can't reach redline rpm in gear and your bottom is clean, check to make sure that the transmission that was replaced had the same gearing as the current one. If all of that checks out, then look to your prop pitch.