Agreed.
In a radio, receive is low load, transmit is a higher load. Size of feed wires and quality of connection can make a difference here.
Crimp connectors with some solder and/or dielectric grease can help. A "U" shaped crimp is better than an eyeball/football crimp.
Assuming Nadler will come in and argue, whatever........

Yes, measure battery voltage AT the radio during transmit to see if you have a big drop in power/voltage. If you do, work your way up the power feed to find where the voltage changes, then fix the connection.

Good idea previously on checking at the radio. ;-)