Slight miss when cruising

so i found another vehicle doing it... we just finished a 46 dodge with a 318/518 and we filled it up about a week ago and its doing the same thing, anything over 38* and it starts that surging BS.

Its our F**King gas...

now this not being my area im going to ask you guys, could the fuel be rated at 91 (or any octane) but have a lower "effective" octane due to the additives they add or removed for summer/winter blends? i would think not and that means they are selling lower octane gas for a higher price and that makes my blood boil. Any way to test octane at home?