Extra part during transmission fluid change?

I have the truck listed above with a 4R70W transmission. I removed the transmission pan and drained all the fluid, cleaned the pan and mounting surfaces and re-installed the pan. I was pouring the fluid that came out into a container to measure it when I found a plunger looking device in the drain pan. I removed the pan again to see where this came from and I can't figure it out. Hopefully somebody on here that knows these transmissions will recognize it. I will add the images of it. Thanks in advance for anybody's assistance.