1993 Buick Century Buick Century Engine problems

Just as a note, the buick was leaking a little clear fluid that was flinging from the belt ever since I bought it, I always figured it was coming from the A/C unit because it appeared to be coming from there and I am not sure if this is relevant.

I had a fuel leak in my Buick century, so I took it in and the sending unit was replaced. It was driven an approximate 25 minutes on a 80km/h road and brought to me at work. I went home for lunch (2 min drive) and on my way back, as I was driving up to a stop sign the car stalled. The next day it missed a couple times at the same stop sign almost stalling. Later that day, my mom needed the car so she went the same 25 min trip on the 80kmh road and back, no problems. Coming to get me from work the car stalled when she was braking down a hill. The day after this (today) I was driving that same 25 min trip on the 80kmh road and when brakind down a hill the car stalled. On my way back the car stalled approaching a stop sign. I began reading online and one persons suggested to test the car by pumping the brake with the car off, then starting the car with the brake depressed and noting if the break softened and how the car idled, the car idled very ruff and stalled, and since then it will only idled for a short time, sputtering and stalling. Regretably, I did not test to see if the car would start before doing the brake test.

Also, after getting the car back from the mechanic, I noticed that the doors would lock after a drove a short distance, which is odd because they doors used to lock right after I put the car in gear.