NFL's Jason Witten Unloading Texas Mansion, Waterslide & Diving Board!

Everything's bigger in Texas ... including the mansions -- just check out the place Jason Witten is trying to sell!!

Now that the former Dallas Cowboys tight end is playing for the Las Vegas Raiders, he's parting ways with his 8,800-square-foot estate ... and this place is SICK!!!

We're talkin' 17 ROOMS -- including 6 bedrooms, 8 bathrooms, wine cellar, movie theater, game room and wet bar!

OH, AND THE POOL AREA LOOKS LIKE A RESORT!

Waterslide? Yep. Diving board? OF COURSE!

It's all located in a very exclusive guard-gated community on a golf course in Westlake, Texas ... about a 30-minute drive from Dallas.

The neighborhood is also packed with other NFL and MLB players. Glenn Beck is also a neighbor.

Got guests? There's an 828-square-foot guesthouse too!

The property, listed by Engel & Volkers, sits on 1.2 acres of land. Asking price -- a cool $4.6 MILLION!

37-year-old Witten just wrapped up a 15-season run with the Cowboys -- he made over $70 million in contract money alone.

Now that he's playing in Vegas, seems he's ready to part ways with his longtime pad.