Shift problems

I have a 2006 4x4 automatic v6 Off road package and tow package. At 123,000 it started trying to shift early at low rpms when starting from the stopped position in Drive. Toyota says new tranny. Transmission shop says torque converter. I have a new Toyota TC installed and all is well for 3 weeks. It starts again. Transmission shop goes through it 3 more times and cant find anything wrong. It actually changes gears before computer is telling it to. It only does this in Drive at low rpms. It works fine in 4 or 3 or low position on shifter and when you give it 25% pedal or more. ANY BODY got an idea? I presently have 150,000 miles now. Another shop adds a anti chatter to transmission fluid and this is a no go also.

 

Transmission shop ran it hooked up to computer. What he told me anyway. I'm not a transmission mechanic but I have worked on hydraulic systems and it acts like a ball seat in a valve isn't seating properly to me. It chatters like a clutch trying to grab without enough rpms. It does this in all gears but only when shifter is in D and low rpms

 

Thanks, Will check into it. Changed my plugs today and one looking a little ruff. It was loose and had oil up onto the hex part and even a little brown on upper insulator. I've been told by another guy possible causes are need of a tune up, variable valve timing solenoid and TC solenoid.

 

Subbed for outcome after tune up is performed. Do the throttle body and mass air flow sensor cleaning while you are there . Here is the how to with pictures
http://www.tacomaworld.com/forum/technical-chat/94203-how-throttle-body-cleaning-2005-v6.html

 

I did forget to mention I have AFE cold air intake, throttle body spaced and exhaust. Will chck that out gear cruncher