The Right Wrong Number -- Jim Nesbitt

If you're looking for gritty, The Right Wrong Number is as gritty as Number 36 sandpaper.  Ed Earl Burch is former cop and now a private-eye.  He can't resist the wrong women, and when he gets a call from his former lover whose husband has disappeared, he takes the case, even knowing he shouldn't.  As it happens the husband has faked his death because he owes money to some people who will be happy to have him killed to get the money back. And because they think the wife might be involved, they'd be happy to kill her, too.  The husband would also like to kill her.  

Soon enough, they'd all be happy to kill Ed Earl, and they do try.  There's a Dallas cop who'd also like to see Ed Earl dead or at least maimed because he thinks Ed Earl is responsible for the death of his partner.  Ed Earl takes so much punishment in the course of the book that it's amazing that he's still able to stand, but he presses on.  

There are some great Texas scenes, including a set piece at the Houston Rodeo, and there's a good bit of Texas travel between Houston and Dallas and out to the Big Bend country.

The Right Wrong Number has a lot of sex and violence in many combinations.  It's dark and hard boiled.  And I've already mentioned gritty.  If that's what you're looking for, this one fills the bill.