2000 VMAX 225 power loss

[jrowe13]

I have a 2000 VMAX 225. Starts and idles great. Runs strong up to about 55-60 then flatlines. I had it out earlier this year with no problems (72 mph top speed). Haven't changed setups or anything. Once the engine tops out at 60 or so, If I jockey the hot foot around a bit I can feel the power kick in and boost me to 65-68, but then slip back down to the high 50s. I've checked my throttle cable and everything seems to move fine. Anyone fimiliar with this issue? Thanks

[DMSOUTH]

Sounds like O2 sensor needs cleaning--also draw tube.....

[jrowe13]

Where is the O2 sensor located? Also, I just remembered that a couple weeks ago I had to run 87 octane fuel in it. Since then, I have ran about 15 gallons of 92 through it. Could that have something to do with it? Thanks