Performance issue with 60 hp 4 stroke - fuel?

[reelblues]

2016 60hp 4 stroke B15-021298
Hi, I bought a used 2016 Tracker 175 last fall after I moved to Iowa from down south last year, so no experience in winter storage. I got it right before I stored it for the winter and only got to take it out a couple times and I remember it running fine. It had half a tank of gas. I added Sta-Bil and put it in storage. Took it out in March and have issue with performance ever since. I added some fresh gas, a few gallons of 91 octane, no ethanol before taking it out and the motor would never get past 4900 rpm with me and about 4600 with 2 people. I’m pretty sure I remember hitting 5500 before storage. It felt bogged down like but no knocking or coughing or anything like that. It never got the stern up and the rear feels really heavy. So, I started working with the prop. I bought a Spitfire 4 blade 14p and have been moving the motor up in increments. It did help the hole shot and a very little bit in rpm, but I still can’t get past about 4900 rpm in calm water at best, but the hole shot is much better but the bow never really gets down right. I’m currently at 4 3/4 prop to pad with one hole left to raise. I was going to try the last hole but ran across the fuel octane article in this forum. I’ve added 91 octane gas 2 or 3 times since I got the boat assuming that was best. At this point I may have replaced the old gas with 91 and I’m assuming the old was 87/88 . The previous owner just told me he used non ethanol. So, one question is could 91 octane decrease my rpms several hundred? Also, I checked the throttle and it looks like it’s moving all the way forward from what I can tell. Anyway, I assumed I had a prop problem but now I’m wondering. I have about a quarter tank of gas left.

[EuropeanAM]

Please check your serial number- it's not accurate (format is digit, letter, six digits).

Need to start running the correct fuel (87 octane). Also need to check the BASICS: Compression, SPARK and Fuel Quality/Condition/Pressure.

Don't change props to try to regain lost performance until or unless you know the engine is running correctly.

I would have a set of new spark plugs ready to go in after the compression and spark test. Make sure all of the other Annual Maintenance is up to date.