There's your problem - you have too much pitch on the prop. WOT rpm is how you figure out if you have the right pitch or not. My guess is that Dingbat is exactly right. Your typical operating weight is probably more than you think it is.
"Kick the tires and light the fires - it time to do some yankin' and bankin'! No wait! You can't do that in a 76!"
???
Sure you can, more so in the 757! Best commercial plane in the fleet.
OK, to wind this up;
Best of Thread award goes to Dingbat. Solid advice from someone who has the same type of boat / engine that I have. Thank you. Thanks as well to the other responders, your input is truly appreciated. I'm picking up a couple four blade props to try out from a good local shop. Working on reducing gross weight, but with the holidays and all...
