5L40E transmission problem

Hello everyone, I have a problem that just developed on my car (listed above) with the 5L40E transmission. While driving the other day the transmission felt like it just went into neutral upon reducing rpm's while decelerating. I pulled over and the transmission would not engage in any of the forward or reverse gears.

However, as I let it sit for five to then minutes when I started the car back up it would engage in every gear and shift normally until it warmed back up, then as before it would disengage to neutral.

Next day, cold start and the car acted exactly the same way. Transmission works great until it reaches operating temperature, then disengages.

Things I have done: I drained and flushed the transmission fluid, replaced the fluid with Dextron VI with a new filter.

My suspicion is that it feels like an electrical or sensor problem of some sort. However, I am clueless about these drive by wire systems. Hoping someone can help me out.

Thanks in advance!