Hello,
That can be due to many reasons. If you would attach your configuration maybe we can see what the issue is.
But make sure that you configured NAT properly and you dont have any ACLs blocking your packets. Make sure your default route is set.
Also use the commands below to see where the drop is happening.
"Packet-tr input inside tcp 1234 4.2.2.2 80 detail"
"Packet-tr input outside tcp 4.2.2.2 80 1234 detail"