Will not go pass 10mph and 1000 RPM

I have a 03 2.5 altima and is been a nightmare I took it to a shop because the car would not go pass 10mph at 1000rmp so they had me replace the accelerator perdal and they also check the throttle finally they told me I needed a new ecm I order a replacement with the same part number and now the car will not start please help also replaced the cam shaft and crank position sensors