Trans gone in 24hrs with no previous indicator. 2000 tahoe
 

I have a 2000 Chevy Tahoe rear wheel drive 5.7 L Vortec that work completely fine on Saturday as no slips no hard shifting or knocking and absolutely no indication at all previously to indicate a problem with the transmission. And then Sunday got in the truck yesterday afternoon to run down the street to pick up my mother and I came to a red light and stop and as I started to accelerate I felt the truck lose power almost like it was bogged down so I left it off the gas thinking it's beginning to Slit a little bit and then give it some gas to allow it to look into gear and give it gas again and it continue the same then slowly begin to accumulate power again and speed and did this maybe six seven times yesterday on a couple different trips through town not too far and so I decided I'm just going to park it tonight and try it again tomorrow see if I can figure out what's going on with you know a little internet research and speaking to a couple of the people. This morning went out and I started it up so I can let it run and warm up a little bit also the evening prior I check the fluid it was pretty good I looked under my car no leaks I'm not a mechanic so I don't know about engines but I know the basics on you know some of the things I can cross off the checklist to inform mechanic about. So I had check transmission fluid and it seemed okay. I had climbed under and looked around no puddles or anything like that I didn't see any slight drips or any other indicators as to intermediate cause. And today Monday I go out and warm up the car go to driveway about 20 minutes later and when I put in reverse and take my foot off the brake no movement so first I look down make sure I'm in the right gear shift back the park come back to reverse again no movement so I give it a little gas nothing no other than the motor no like obviously odd noises like grinding or clunking or anything like that so I lightly touch the gas pedal holding it at about 7:50 to 1000 RPM thinking it might take a minute to slip into gear I do this three or four times nothing. So I put it in neutral at throttle a few times let it sit for a second and then shift down and try to put it in Drive and slowly take my foot off the brake with the same result. I've had a few cars with transmission issues before but I've never had a car or I've ever heard of a vehicle that had no previous slipping hard shifting time delays between put it in gear and engaging or anything else like that 2 having it happened one day you know a few times and then the next day the transmission not work at all. Does anybody know what this is

The first thing I would look into is the transmission vacuum modulator. I had one go on a different vehicle once; the fix was relatively simple and inexpensive. Plenty of Youtube videos on that as well.

It's a 19 year-old-truck that has an automatic transmission that has possibly reached a service life limit?

The good news is that they aren't too hard to swap.

You might check all your fuses in case a circuit isn't working. Any dash lights showing that didn't before?