Need help with diagnosis. Truck stalls. Transmission is making a weird sound.

Having issues with my 2004 Prerunner 3.4 auto 2WD 195k miles. Truck was idling funny but driving ok. Then on the way home, it cut out at a stoplight after I came to a complete stop. I restarted the truck and it died again. On the third try, I restarted the truck and this time kept my foot on the brake while I also gave it gas. This worked and I was able to drive the truck home. When I go got home I put the truck in reverse and it died. When the truck is in drive or reverse, you hear what sounds like some small pieces of metal moving around in the transmission. I think there's something wrong with my transmission but would it cause the truck to stall and die? When would be the best way to figure out what's wrong or if the transmission is going? Any help or advice would be greatly appreciated.

 

How old are the spark plugs and battery? 9 times out of 10 it's something electrical.

 

Battery is 4 years old. It's been a couple of years since I've replaced the plugs. But the tranny is making noise that I've never heard before. I can get the battery checked to see how well it's holding a charge. I can pull the plugs. Hopefully it would be either one vs tranny issues.