New engine control module

About two weeks ago I took my car to a mechanic because I noticed that whenever I would press the gas petal to accelerate while getting onto the freeway that the car would barely go up to about 2,500 rpm's no matter how hard I pressed on the gas, therefore it took longer to reach the required speed. Code reader said it was a problem with the throttle body sensor performance. Had it cleaned out, mechanic told me that I needed 2/4 fuel injectors and a petal position sensor. Well, when I started my car to leave from the mechanic's, my car was ten times worse! When I turned the car on the rpm jumped clear to 3,000 rpm's, stayed that way for about ten seconds, idled down and the engine began to run very rough, making puttering noises. Also, noticed a slight decrease in fuel on the fuel gauge. While driving the car would accelerate slightly by itself. Had the car parked for about five days, when I turned it back on it was running fine but noticed when I braked that the brakes would lock and unlock, making the car jolt repeatedly to a harsh stop. Took it to a well known, supposedly reliable mechanic (I have trust issues). They told me that they individually tested the fuel injectors, the ABS, the pedal position sensor, along with other components of the car with a tool that could control each of the parts individually, telling them what to do, and they all worked perfectly. Therefore, they came to the conclusion that my problem would be with the ECM, which makes a lot of sense to me, actually. Only problem is that they want to charge me over $1,000.0! :( Found that a ECM for my car is around $200.00 on the GM parts direct website, and that replacing a ECM is very easy, although I would have to pay someone to program it for me. So, I am really looking for a second opinion. Does this seem to be the problem? I do not want to waste my time and money!