The ECM is located behind the parking break pedal. You have to access it from under the hood. You can see the harness going to it under the steering column. You may have to partially remove the inner fender well to pull it out.
You will not be able to see it from inside the cab. It is behind the aliminum dash support bracket. It's the one closest to the driver-side fender. You will see a stud with 10mm nut just above the harness. Back the bolt out of the center of the harness, then remove the 10mm nuts, one on top, one on bottom. Then you can pull the ECM out of it's pocket.
No problem! You may be able to get it out without moving the inner fender, but I had to take all of the screws out of mine from the 12 o'clock position down to the 4 o'clock and pull it down. Good luck and make sure you clean the contacts good.