Recreational Vehicle Lpg Tank Valve/gauge problems of the 2013 Nissan Sentra

My car would start to jerk as I was driving, I went and got it looked at and the auto zone guy said it was the voltage regulator in the alternator so I had that fixed, then the motor mounts had to be replaced. After allthat it was still jerking and it is my alternator. I drove my Nissan off the lot with 298 miles on it and the transmission is slipping. I called Nissan and they said they would not cover it because im at 101k miles even though I have the security +plus contract and there is a stipulation with kentcuky. There should be absolutely no reason as to why a 6 year old car is having so many issues all of a sudden. It literraly started a month ago and is due to be paid off in July. When I pull off from stationary sitting it jerks, once I coast to a good speed around 50mph and up then it wont jerk but hesitates and my rpm gauge jumps up and down.

When the vehicle's gas gauge is indicating the fuel tank is empty, after refueling the gauge does not indicate the change. This is a fairly new car, I don't think this should be happening already! I will run out of gas, and it will be because my car isn't telling me the right amount of fuel.