Tech II,
Thank you very much for your input. Unfortunately I do not know if the truck was driven with diagnosis tools attached. But I did reiterate several times to my former mechanic that simply hooking the truck up (statically) to a code reader was not what I was looking for. I needed/wanted someone to drive the vehicle, in traffic, on the highway etc... - to get a complete understanding of the issues. Apparently that was not done because when I was notified it was ready for pick-up and that it was running "great", it almost immediately began exhibiting the very same issues.
I am going to do some research on reliable and trustworthy technicians here in the Lubbock area. I would welcome recommendations should any forum members know of a mechanic they trust. Failing any direct referrals I will certainly consult with a local GM dealership for further exploration. I firmly believe that it is not a transmission issue and that the erratic gear changing is simply a response to varying output torque from the engine.
In researching this issue further I found another forum where someone was describing somewhat similar issues (with a larger emphasis on the idling problem and a GM technician offered the following possible solutions to consider:
Check for air leaks in the Air Induction system (e.g., in the intake manifold)
Check for air leaks in the PCV system and in its related hoses and/or valve
Idle air inlet passage or throttle bore is dirty or full of deposits
IAC valve has failed
MAF sensor is dirty, "skewed" or installed improperly
Throttle plate, throttle shaft or linkage is damaged or sticking
TP sensor is out-of-range or "skewed" high
I would hope its not the last issue as my TP sensor was just changed.
Thank you again for your time and advice. I welcome any additional input you may have.