Hard shifting/Transmission jerking

I just purchased a pre-owned 2017 Jeep Renegade Trailhawk 9-spd, and after about a week of driving it, I started noticing the vehicle was having issues shifting gears. At times the RPMs go higher than usual, at times I can’t accelerate, many times this is followed by a jerking that feels like the car is getting hit. The gas mileage at best is 16mph (not sure if this is related or normal for this vehicle; it’s just lower than promised). At this point, the vehicle is almost not drivable which is disappointing because I really loved it at first. Unrelated, the Connect system also doesn’t work because it’s a 2017 and there is no fix.