Okay guys, I have a 1996 A5, 2.8L V6. First gear, fine until shifting. As soon as I press on the clutch, the car seems to immediately slow down, like the engine is being forced to slow down. Then, in 2nd, I get practically no acceleration when I have the pedal to the floor (same with 3rd and up) and the car feels like the brakes are on (but the brakes aren't even being touched). The tires even squealed at one point, as if I was pressing the brake, but I was not. When I pulled over and went to try the car again, I accelerated fine, no bogging/slowing down, got all the way to 3rd gear fine. However, when I went to turn around, the acceleration issue happened again.

I'll note, my muffler is completely off due to previous owner. Not really sure if this is back pressure from having no muffler, or bad brake calipers, or something transmission/engine based. Anyone that could provide any insight would be a big help!