2017 Chevrolet Silverado 6L80E Lost First Gear. Fix and Walkthrough

Headed to work, lost 1st gear without any other issues. Like other GM transmissions I could manually select 2nd and start off in 2nd. So, was at least able to get home. Fluid looked good and the truck seemed to pull fine while in 2nd. All other gears worked like they should. Once disassembled, I found the 1st gear plastic ball check to have been chewed down to a much smaller diameter and became jammed in the valve body separator plate.
Found quite a few good videos showing different parts of this fix but not one to really show the whole process. Hope this helps. But I'll also paste the videos I found most useful to help you troubleshoot and hopefully repair your transmission. Please comment any other suggestions.
First here's all the parts I bought for the job. These are all GM parts as that all I had access too.
◦ Valve body plate and check valve
◦ 24272467
◦ Temp Bypass Valve with o rings and gasket per TBN 21-NA-199
◦ 85585333 - TBV
◦ 23277649 - x2 - O-Rings
◦ 85628205 - Gasket to Transmission
◦ Filter and seal
◦ 24236517 - Filter
◦ 24225347 - Seal
◦ Gasket
◦ 24224781
◦ Fluid
◦ Dex-VI 2 gallons
Need 7mm, 8mm, 10mm sockets, a ratchet, and a torque wrench.
However, you will need a specific socket for the 6 bolts retaining the valve body.
The small socket set I bought called it an E12. Like an External Torx.
GM part number is DT-48285
Snap-On 10EPL.
The GM and SnapOn seem to refer to it as E10. Why the one from the set I bought called it an E12... I don't know.
Socket set from Oreilly Auto:
www.oreillyaut...
Also note this socket set has very deep concave on the face, and I had to grind the socket flat to work properly.
Alternate TBV:
ppepower.com/p...
Sonnax Torlon .250" Checkball Part No. 10000-08:
www.summitraci...
~~~Videos for further reference~~~
This was the first video I found to mention the issue with no 1st gear and suggested to use the Torlon balls:
• Silverado 6L80e 6L90 N...
Good video showing the removal of the transmission pan and changing the fluid:
• GM 6L80 Transmission F...
Good video clearly showing the removal of the valve body:
• 6L80/6L90 valve body r...
If you just wish to modify the TBV:
• Keep your 2014 - 2018 ...
TBN 21-NA-199 for the TBV to keep the transmission fluid cooler:
static.nhtsa.g...
One more thing to note. The TBV can come with different style line connections. Please verify which TBV yours needs if you need to replace it.