Prop Question - Running at high altitude

[Off Trail]

Hello - First time posting on the forum but I've already found a ton of information by searching. I have one problem I haven't found an answer to yet -

I recently purchased a used 1997 SNOB with the GT 40 Pro Boss, with only 260 hours according to the meter. The engine seems to run strong and I just did a full tune-up (Plugs, wires, distributor, oil change, injector cleaner, fresh gas etc.). I am in Steamboat Springs, CO and have had the boat out at ~8,000 ft altitude on the lake I will typically be on.

My top end yesterday was as follows:
Top Speed: 39/40 mph
Top RPM: 4,500

I'm assuming i am over propped for the altitude, at least I hope that is the issue. The prop is an OJ Legend, and the only other markings on it are "10 97". Anyone know what prop this is? The boat also came with an OJ 13 16 P Cup that looks like it has never been on.

Any recommendations, thoughts, etc?

[jhersey29]

I have the Acme 422 in Denver and top end is 40 to 41. 1999 Ski Nautique GT40. I had issues when dropping to 4000 feet in Powell. Extra power was nice but not needed. Boat started hard for 3 days then was good to go.
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[Off Trail]

Thanks jhersey. What RPM are you getting with the 422?

[jhersey29]

I'll be out tomorrow am. I don't run top end very often so I can't remember. I do know 2900 is 28.3. 2950 is 28.6, 3150 is 30.4, 3350 is 32, 3575 is 34.4, 3600 is 34.8. I know those because that is the Stargazer Rpm and GPS for most of my ski group.
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[jhersey29]

2 people, half tank gas, 4700 rpm, 42.8 mph, 1999 ski nautique, gt40, acme 422
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[Off Trail]

Thanks for the info. I'll have to do some more digging to find out what might work for me at 8,000.