car seems to jerk when idling, and jumps violently when shifting gears

I recently had my CV joints and break pads replaced. Since then, the car seems to jump and jerk around. The problem is not consistent. When climbing a steep hill, it will often shift violently to accelerate. Other times, it seems as though it's working extra hard to accelerate at all, like it just can't shift gears. When it finally does shift, it is often jerky and occasionally extremely violent, like I'm being thrown into the back seat.. When stopped at red lights or sitting in park, I can sometimes feel the car jerking as if it's moving forward in short bursts, like a rocking motion, although I can't tell if it's actually moving or not. It's almost as if it's trying shift gears at times where it makes no sense. Sometimes the jerking is worse than other times. There appears to be no consistency, although this was never an issue before the CV joints and break pads were replaced. I'm not sure if the problem worsens when the gas is low, but I do seem to notice it more when it is. I have had gas tank problems for some time. Even if the tank is on empty, the pump will shut off as if it is getting splash back, like the tank is full. I'm unsure if these problems are related.