Loses power going up hill and jerks on hills sometimes

I recently bought this car, it had blew the intake on the previous owners and they had it fixed, but it did set awhile before I bought it. They sold it because the brake lines were rusted out and didnt have any working brakes and the abs light was on. I drove it home using the e brake. My neighbor who is a mechanic fixed the brakes and the abs light went off. Then shortly after we had to buy a new starter, and battery. After that the car ran really good no problems, no lights on. Few days later the service engine light came on and stayed on. My neighbor thought it could be an o2 sensor. I went to fill it up and when it got full gas started coming out all over under the car. So my neighbor had me refill it so he could see where it was coming out. We ended up having to get a new fuel pump sending unit o ring. Fixed the leak drove it about half a mile check engine light went off. Now no lights are on but now the car loses power up inclines and will jerk sometimes. I live in a hilly area there is no other way around going up hill. It also hesitates to shift sometimes going into 4th gear. The trans fluid looks OK and is full. Not sure what the problem is either does my neighbor! PS it runs fine any where else other than hills. Sorry so much info probably more than you need. Just want to be thero as possible! Please help!