Galloping Thunder (1946)

The cattle herds of some Arizona ranchers are being stampeded and stolen, so the Arizona Stockmen's Syndicate sends ace investigator Steve Reynolds in to find out who is responsible. Steve poses as a vicious gunslinger named Buck McCloud to work his way into the gang, and then becomes the Durango Kid to disrupt the activities he learns about. Jud Temple is the loyal fiancée of town banker Grat Hanlon who turns out to be the brain-trust behind the gang.

Unfortunately the movie Galloping Thunder is not yet available on HBO Max.