2005 Lexus IS 300 Acceleration after major accident.

Hello. I was recently in a pretty bad accident. Between the body work and the mechanical, the repairs came to $10,330. People have told me that the car will never be the same, but the thing I'm noticing now is pretty disturbing. It will drive normal for a few minutes, but then it will suddenly feel as though the accelerator stiffens up. It's very hard to explain. The car will almost feel like it's going to stall and it will take a decent amount of pressure on the accelerator to pick up speed again. In the past, you barely had to tap the pedal and the car took off. I'm pretty unhappy with this body shop (a large, commercialized one that Lexus sent me to) because they broke things that weren't broken in the accident (sun visor and key fob). They had the car for 3 and a half weeks and I didn't bug them or complain about anything. When I had the accident, there was almost a half tank of gas in the car. When I picked it up, it was on empty and the fuel warning light was on. I went to the nearest gas station and then the gas tank release wouldn't work. I had to have someone pry it open while I held the release up. I went back immediately and they fixed it (missing spring) but I didn't discover the other things until after I left again and then they were closed so I have to wait until Monday. But I'm not sure if this accelerator problem is one of those things that will never be the same, or if it's something that should not be happening. I really don't like driving the car now. It doesn't feel safe to me. And the fact that it will drive fine for a little while, and then do this, and then be fine for a little while again, does not seem right. If it did this when I was on a highway going 75mph, I'd probably have a heart attack. I've only taken it up to about 60mph since I picked it up. Also, the mpg needle is all wacky. It jumps around constantly, even when I am maintaining speed, and it never did that before. If I have to bring it back to them, I'd like to have at least some idea of what I'm talking about. Mainly because I don't trust them.

Thanks!