If you know nothing about cars pls dont continue reading
My car is a 2004 Mazda 3. I've bought it at a dealership at 130k miles for $6,000, perfectly serviced, and is now at 136.7k. Some history is that I got my muffler changed to flowmasters a couple of months ago. I've done an oil change recently. Whats also weird (Don't know if this is normal and relevant) Is when I drive past 1st gear up to 2nd, and I let go of the gas petal, it makes a weird whinny sound. I can also switch gears perfectly. The problem is that my car is perfect on 1nd and 2nd gear. My Engine starts up pretty smooth, and if I revved my car in neutral or in park it sounds perfect. Since its winter time, my engine is still cold when I turn it on. It works and drives perfectly, but when it warms up, it starts to ferociously jerk when I get into the 3/4 gear. Its exactly at 2k rpm. Works perfectly below that, and can't accelerate past that (unless the car momentum somehow gets to 60mph my car will accelerate, but it wont show my car reving). My car would then drop back to third gear and play around between the 3/4 gears. What really sucks is when I don't have enough momentum to go up a hill, I go so slow that I'm forced to turn of my car so i can return back the 1st gear and drive up the hill. I've checked my transmission fluid (when it was off because i accidentally broke my hood release) and it looked light brown. I know I'm going to need my transmission flushed, but I want to know the real problem before I start spending loads of $$. My AT light also comes on 50% of the time I drive the car. I will take it to get diagnosed soon, but I want to know how much I would roughly be spending, because I plan on getting a new car and Idk if i should invest any money into the car. Thanks!