WOT RPM & Prop question

Hi all,

I have a 92 Supra Esprit,(poor man Combrio) looks & runs well.I am the 3rd owner. I have the original or same as original prop on it (13x13 OJ legend) in good shape. Hole shot is great & pulls strong.I dont make a habit of running my boat at WOT but wanted to find whether top speed was within 44-4600 rpm range. With just myself in the boat I reach 35mph at 4400 rpm. GPS verifies this.That seems a bit slow for this boat I think it should be more like 40mph. However WOT with this prop is 5000 which gets me to 42 mph. I only did this once for a very short time. Surprised at this being a factory spec prop. Is this a prop issue or something alse?

Time to find out if your tach is right.

I considered that just after I posted this thread. It would be great if the Tach was misbehavin" Inexpensive solution. I'll get ahold of a shop tach & test it.