You cannot run 87 octane fuel in an engine with a 10.5:1 compression ratio. You MUST run 93+ or you can cause serious damage long term.

What you may be experiencing is severe timing retard to compensate for knock (detonation).

 

Thanks guys. I'll fill the rest of the tank with Supreme and see what happens. I should've known better. Even if this isn't the full problem it's gotta be one of them.

 

I would put unleaded high octane racing gas in the rest of the tank and see if it goes away...if it does, try running premium and see if it stays gone, if not you have some detonation issues...