Sorry for the delay. Yes. This does sound like an internal issue the transmission.
More then likely the pump is not operating or you have cut seals that is allowing the pressure to bleed off rather then build to the proper level to allow the transmission to engage.
Basically the clutch packs inside need to be applied with a force of fluid pressure and if the pressure is not high enough then it will not engage the gears.
The best way to check this is to check the fluid pressure with a gauge and then do what is called an air check which is basically applying a low pressure of compressed air to listen for the clutches to clunk which shows they are sealing. If there is no clunk then it is a clutch pack issue.
As you will see in the info below that a no drive situation can still occur even with correct pressure so we need to make sure the air check is done to confirm this.
Let me know if you have questions. Thanks
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Monday, April 5th, 2021 AT 5:58 PM