2002 Monte Carlo SS Transmission slip

Transmission slips on left turns and once its driven
for 30 mins it will start slipping when driving
straight also. When im going down a hill if i
attempt to reverse the tranny will pull i can pull out
of a hill but it will pull bad the whole time im sure i
need to replace it with a new one my friend has a
04 monte trans. Just wanting other opinions on it
not smart on cars.