Got a 2000 Chevy silverado with. 5.3 backed by a 4l60e.
Cold start the truck goes in every gear fine and doesn't slip at all. A few minutes later it Just quits on me. Will loose all gears including reverse. I shut it off for a few minutes and suddenly have every gear back like nothing will even do a full burn out and drive then bam I loose Every gear.. any help will be much appreciated

 

it's that worn out converter valve thing in the valve body.
The valve body needs to be reamed and oversized Sonnax valve installed.
Or the few other valves that fix it, Superior Products, TransGo, etc.