I have an 01 Sierra C3 (denali) I installed a Lvl 5 4l65E with yank sst3200 about 8,000 miles ago. At random it would get stuck in 3rd gear and SES light would come on. Pulled the code and it would say "Shift solenoid B stuck Open". Shut truck off, wait 30 seconds, start back up fine to drive. Drove around like this for about 2 months since I was in germany. Truck is back in Connecticut now and I brought it to a shop. They narrowed it down to every 4th start it will get stuck while driving at somepoint.
The shop replaced the shift solenoid twice. Said after the 2nd one it was good to go, wife picked it up drove it home, next day drove it to work and same crap happened. Brought truck back, to shop like WTF?!? Mechanic stated "while driving it I had it hooked up to my computer and when I raised the pressure it would shift fine so it must be something in the valve body". So I said ok drop the pan and figure this crap out, they did and wife picked it up again and told her that they replaced the shift pressure sensor. My wife tells me when she comes to a stop and goes again the first time it shifts is incredibly hard and violent. I'm assuming it's still the 2nd-3rd shift.
What I'm thinking is the mechanic went into my tcm and adjusted the shift pressure for that shift to much harder half-A** fixing the problem.

What is your opinion on what could be wrong or what I should do. I was thinking have it brought to a diff. tranny shop and have them look into the tcm and let me know what the shift pressure for 2nd to 3rd is and I can ask my tune guy (westers custom tune) if it's altered from what he had it.

 

The problem is you dont have a problem, The 2-3 shift solenoid code is the PCM being confused by the stall converter RPM it thinks the 2-3 shift did not happen and then sets limp mode. You can change the solenoid till dooms day and it will come back. They likley raised the line thinking this would stop it but it wont, The only cure is to delete the test for the code PO767 in tuning

 

Ok I was just refrenced this on another forum.
"If this is an intermitant problem and clears up after turning the car off and the car begins starting in 1st again it maybe what some call a stall code, Basically the PCM is confused by the stall converter,And will set that code even though theres nothing wrong , You can replace the solenoid first however if it continues to happen you may need to have the test for that code removed from the PCM"

"Go into HPT (HP Tuner) and turn the codes off for those two and you will no longer have problems. The PCM detected slippage (convertor) at a given RPM and disables shifts into 3rd and 4th and unlocks the convertor permanently until the engine gets shut off and restarted. If you drive it too long like that you will fry the transmission." (p0757 and p0751)

Is getting rid of those codes something a regular tranny shop can do??

 

Thanks for the help Frank. To the op please give me a call and we will get you through this.

 

You are certainly welcome

 

I had this same issue after I installed my FLT Level7 and Cirlce-D 3k billet multi-disc. Contacted Justin at BlackBear and he turned off the code(s) that the PCM may set due to the slippage of the higher stall converter, and it's been fine ever since. There are a few adjustments that need to be made to the PCM logic when a built trans/high stall converter are installed...things that come to mind are turning off adaptive learning, setting line pressure back to stock, and maybe adjustments to the shift timing (as well as turning of shift solenoid codes)

I'd be careful driving around in limp mode too much as I'd assume that it can't be good for the 3-4 clutches

 

Great info.