Help Me..

2000 LS2

Here's the downlow on my vehicle:


My vehicle was having problems shifting. I guess I would describe it as "rough shifting". The SES light was on and I took it to get it checked out.
They reconnected the ECM and everything was peachy until it came back on and my she started to shift in the same manner.

So now I'm thinking I need to reconnect the ECM again and make sure it stays connected.
Problem being is that I have no clue where it is
I've worked on a few other vehicles but I really don't even know where to being on this beast of a vehicle.

Help... please.

Background Info-

Work I've gotten done to Lola (my vehicle):
Water pump, coolant bridge and thermostat replaced because of failer/ leaking. Sparkplugs, timing belt, idlers and tensioners, trans and air filter also replaced.
The previous owner didn't really take care of Lola the wa

 

BCM: is up behind the glove box

ECM: is at the base of the windscreen in the cowl under the hood