Improper box or poor location/placement of the box in the trunk.... assuming he doesn't have LPF on HU or amp set @ 50hz or something.
Old school stroker has been used as PA driver and playing well up above 100hz shouldn't be a problem at all in the proper box.
So off your factory HU are you using a line out converter or like the hi input on your boss amp?
Also, coming from a stock radio, he's more than likely not crossed at all on his mids. They should begin to fade under 100hz and the sound should balance. If this was a fully amped setup with complete tonal control, I would suggest finding out all the parts before finding crossover points. On setups ran by people with little to intermediate knowledge, 63-80hz is a great "standardized" place for the LPF for the sub stage.
2). What is the amp's model number? "Boss 2000 watt" doesn't tell us much, but I would look it up for you with the actual model number.
3). What are the dimensions of the box, including the port area, and if you can, length?
Boss CX2000M 2000W Max Monoblock Chaos Exxtreme Series Amplifier
I doubt a dual 2 ohm sub would be paired with that amp. You can only run at 4 ohms. It's not 1 ohm stable. Those dimensions only come out to 2 cubic feet without subtracting any port volume. You didn't mention any port dimensions. I'm just trying to see what you're working with to think of ways to help.
Turn that crossover all the way up (130) hz and see if anything changes. If you're getting highs at that point, dial it back to where it sounds the best and stop. With factory HU and speakers there's no way to cross anything over except the sub, so just set it where it sounds best.
Op some songs don't have "bass". It's part of music.... Lol
OP have you checked your crossover settings yet?
& yes they do have bass. When i had my old setup kicker cvr 12 on those songs it would hit the highs way better than this cerwin vega. But i do love this new sub to death it slams the lows amazingly just wish it would do the highs too.