I am having car trouble pleeeease help?!?

ok so i just bought a 2009 ford escape 2 months ago. I didnt get a warranty, i signed an as is form, although i was never told that the car had a problem. It turns out that i have a problem with the the transmssion fluid. Fluid was leaking and god knows how long i was driving with little to none transmssion fluid. My mechanic thinks this could have affected the transmission. The initial reason i took it to the mechanic was because my cars rpm goes from 1 to 3 for no reason. I know that the rpm naturally goes up as you accelerate. But ill be going 20mph and the cars rpm will go from 1 to 3 causing a jerk thats extremely annoying. It jerks about 10 times during a ride around town. the leak was fixed but the jerking wasnt and my mechanic couldnt say what the problem was. Could it have been because i drove the car for around 2 months with a leakage i didnt even knowing about, causing the transmission to go bad? i sure hope that thats not the case because the stupid people i bought the car from could care less about the problem. im not trying to gain pity but i saved up 4500 for 3 years that i put as a down pymt, spent 1000 to get the fluid problem fixed, go to school and work and rely on transportatoin and if im gonna spend 15k on a car i expect for it to work!!!! im totally broke right now and wanted to trade in my car for a new one at another dealer but i would only get like 1000 dollars once the car is paid off by the dealer since i still owe 11k...all my down pymt went down the drain..3 years of saving up for nothing :( im sooooooooo upset idk what to do. I just want to take my car to the dump. anyway anyone know what could be causing the rpm to go wack?