1980 Chevy Impala My car wont start when the motor is hot

Hello, are the battery cables ok? I'd make sure all connections are clean and tight on both ends. If there are any extra grounds, like from engine to firewall, I'd check that also. Maybe a starter issue?? Did you try to jump the starter solenoid? There could be safety issues, doing that, not so much with an automatic. Just make sure the tranny is in park or neutral and the e-brake is set.

i just replaced my cables and they are clean and tight
i have not tried to jump the starter solenoid but as i try to start the car it gets weaker and weaker but the battery is good could this be the starter cause like i said it is a new battery

Yeah, it could be the starter, can't tell without testing. With a no-load test, the starter may work fine, then go the other direction when you put a load on it. Some of the national brand autostores will check starters for free. You just have the hassle of removing the starter and taking it down there, if everything checks, you replace the starter again.

If I can't get the starter to act correctly on the vehicle, I take it off, lay it on the ground, use jumper cables for a no load test. If the starter won't do anything, I think it is the solenoid or starter.

i took it to advanced auto and it was fine so i dont know what to try next

The small purple wire at the starter solenoid, should be hot with the key in the crank position. Do the testing when the starter refuses to crank. When the starter refuses to crank, can you turn the crank by hand? Something doesn't add-up?