I have a 03 cts that will randomly start shifting hard and at times will display service idle system, reduced engine power, and has codes p2135, p0121, p0221, p2176, p1779, p1780, p1795, i have replaced the throttle body with a new oem one, and have replaced the connector at the throttle body with a new oem, i have performed a idle relearn but i am not sure if it took or not, replaced the trans computer with a used one from ebay, some things i have read show a possible ecm failure and a possible tcm failure and it is a very random problem sometimes it will be fine for a week or even a month it is just a very random issue

When you replaced the connector, did you solder the wires together? Have seen a lot of shops crimp the wires together. Soldering wires together is a must especially for drive by wire systems.

no i did not solder them because at the local chevy dealer they told me to use the heat shrink connectors that came with the kit that had the connector and pigtails in it

You really need to solder the wires instead of the crimp connectors. The drive by wire system are really finicky when it comes to changes with resistance.

I will try that this weekend and by any way do you know the relearn process thanks for the help

Ensure that the following conditions are met:
◦The vehicle speed is 0 mph.
◦The accelerator pedal angle is less than 14.9 percent.
◦The battery voltage is more than 10 volts.
◦The engine coolant temperature (ECT) is between 5–60°C (41–140°F).
◦The intake air temperature (IAT) is more than 5–60°C (41–140°F).
 2. Turn OFF the ignition for 30 seconds.
 3. Turn ON the ignition, with the engine OFF for 1 minute.
 4. Turn OFF the ignition.
 5. Clear DTCs as necessary.

Thank you very much my fingers are crossed