Ayybee09

Hello everyone i have a 2013 Audi A4 with 15k on it. I bought the car at a car auction so the car is salvage. The car was hit threw the back btw.Never noticed that it would take a while to reverse until one day it took around 5 seconds to actually engage. The car was on park and when i put it on reverse the car didn't move,until like 5 seconds later. I have also noticed that when i am on a up hill and the car is on drive it tends to move back a little before going forward. When i noticed this like 2 weeks ago i started to look it up. My muffler is kinda crooked so i read that maybe the pressure isn't giving the engine enough power. My car has no check engine light on and i would like to know if anyone can help me tell me what it is. Thank you for your time guys.