Engine/fuel problems

My dad has the car listed above with a v6 supercharged. It is a four speed automatic transmission. I have notice it has a slight miss going up hills when rpm's are low and at low speed, after that it is fine, but then I put $10.00 of 87 gas in it and after that it is missing very very bad, like it is running out of gas, jumping type. I am hoping I just got some bad gas or water in my gas. I hope it is not the fuel filter or fuel pump. I bought some octane booster tonight but cannot fill the car up until tomorrow when I get paid, because I was going to fill it with 100%gas. They say that octane booster will absorb the water that is in it. Hopefully since it is just below a quarter tank I can just go ahead and pour that booster in and fill it up with 100% gas on top of that. The check engine light has been on also. But I think it has been on for as long as I can remember. I think since it has a supercharger on it and my dad always runs 87 gas in it, it is just not enough octane is why that slight miss was happening and like not having the power it should have. Could you please give me some advice? Hopefully the good news of just adding this booster and filling it with good gas, lol. Thank you for your time.