Car starts and shifts but won't move.

if it shifts then it moves, i dont understand

2007 3.9L Impala started losing power as it warmed up. Coasted t a stop, but now car won't move. Once it cools off again it will move for a short time only. Already had a transmission rebuild. Over 168000 miles on it. I keep it turned up. Oil changes filter changes. But not spark plugs yet, bought second hand. God don't say it's the transmission!

It will only move for a short period of time. Once it warms up, I lose engine momentum and cost to a stop. It will not move again until the engine cools off. Very strange.