Sounds like the fuel tank or fuel pump may be leaking. I’d address the fuel smell in the cabin before doing anything else.

At first, everything was fine. He replaced the master brake cylinder and i don’t need to push all my weight on the brakes to slow down anymore, which IS nice.
But, on the 3rd day, it started having issues on both the highway, and on any street that has even the slightest amount of elevation. If my car is on either one of those two for anything more than 15 seconds, I can be flooring the accelerator, and see and hear the RPMs working hard, but my car will begin to slowly lose speed, overheat (obviously), and – depending on how long I floored the accelerator for – will stall out on me.

On the 8th day, i had gone to work his side streets, everything was fine, but when i was about to head home, i turned on my car, and usually, the carburetor takes anywhere from 3-8 minutes before idling over, but after waiting for 25 minutes, it never idled over. I turned off the car, waited about 2 minutes, and tried again, but again, waited another 15 and still nothing. Frustrated, irritated, and drained from my work day as well, i said “f this” and drove the car home as it was.

Today is the 10th day of me having the car back. A few hours ago, I went to check up on my car, and see what mood it was in. I started up the car, and was about to light a cigarette while i waited for the carburetor to idle over, when all of a sudden, the inside of the car cabin smelled like if i was SUBMERGED in gasoline. It was so strong that within seconds i was overwhelmed out of the car, my eyes were tearing up from the fumes. i did reach back in the car and shut it off. I recollected myself, and checked as much as i could on the outside. There were no fluids dripping onto the ground underneath my car neither fresh or recent that i saw, but my car was sputtering again, and unfortunately, i couldn’t even find out if the carbeurator ever made it to the idling stage, kuz i had to turn the car off.

I know it’s a lot of context and information, but i figured the more details i give, the easier it would be easier to solving. Thank you for your time!

Make sure you’re up to date on all your maintenance, including spark plugs.

Is the check engine light on? How many miles does it have? When was the last time the spark plugs were replaced? Is it up to date on all its other maintenance?

I’m having a similar issue with my I30 I just started having issues when I hit 120km/h then it gradually got worse

I don’t know. Make sure all your regular maintenance is done like the air and fuel filters. You could do a compression test to check to make sure you don’t have a problem that’s leaving you down on power.