well I am going to attempt to change out some of the parts that may be causing this code. ONLY the ones that do not require removing the valve body. I have some questions about the selonoids and the new Sonnax valve with the teflon washer.
First I know that the 2 selonoids for the 1-2 and 3-4 gears are the same ones.these look like they would be easy to find and change
The next is the TCC PWM selonoid. IS THIS ONE SELONOID? or two seperate ones. and how do I know which one it is,
The third thing is the TCC selonoid and the new wider valve I think its Sonnax 77805E-K. I am under the impression that it does not need to be reamed out to install this. I dont want to ream the bore. Please tell me I dont have too. I also dont know where this is located on the valve body. I hope the body does not need to come off.
If someone has a picture or diaghram they can refer me to that show where all the parts i listed are located that would be a big help.
If therer is anyone that can guide me through the process of replacing these items it would be appreciated. I know its a long post but wanted to cover as much as i could. This is on a 99 blazer thank you.

 

I have this bookmarked in case I ever own an automatic.
Might be some info that can help you.

Complete rebuild of a 4L60E:
4L60E Repairs

 

I just recently replaced the valve body on my '96 and while I'm not absolutely positive you can remove the A & B solenoids with the valve body in place, but it really looked like you could though. Theres only a spring clip on each one holding them in. You need a pick tool or hook to pull it out. Might be smart to hold the clip with you other hand as they sometimes like to fly once you pull em' loose. Refer to the 1st attached pic.

2ndly - The PWM solenoid is just one part. It can definitely be removed (same way as the A & B solenoids) without removing VBody. refer to 2nd attachment.

3rd - I don't know much about the Sonnax apply valve but I couldn't see how its bore could possibly be reamed with the VBody in place. Plus, I think the clip holding in can only be remove from the business side of the VBody. The TCC solenoid is trapped above the PWM solenoid which must be removed in order to get the TCC solenoid out. Plus the TCC solenoid is hard wired (no detachable wire clip) so youll have to splice a new one in unless you buy a new complete wire harness with the TCC solenoid already attached. 2nd pic again.