Death Rides the Pecos — Brett Halliday

On the road to easy living, Twister and Chuckaluck ride straight into a heapin' mess of mystery and intrigue

Twister Malone and Chuckaluck Thompson can't catch a break. These two wisecracking friends -- the first lean and clever, the second stout and tough -- have ridden together from the Rocky Mountains to the deserts of West Texas. All they want is a trail to follow straight through to Mexico, where a ranching job offers honest work, peace, and quiet. But no matter how fast they ride, trouble keeps hot on their heels.
 
A gunshot breaks the silence of the lonely wagon road. By the time Twister and Chuckaluck reach the corpse, the killer is long gone. In the victim's pocket they find a letter from a woman begging for help, a woman whose savior now lies dead in the alkali dust. Twister and Chuckaluck have no choice but to take up his mission -- even if it means facing down the quickest draw they've ever been up against.
 
Death Rides the Pecos is the 2nd book in the Twister and Chuckaluck Mysteries, but you may enjoy reading the series in any order.