I`m quite partial to the Chevron Delo 400 15W-40 if you really want to use a 15W-40. I used it in my 93 Ford Ranger 4X4 4 liter for about a year, with good results. The vehicle now has 145,000 + miles. However I have recently went to 5W-30 S3000 Amsoil, as I decided I didn`t need a 15W-40. I don`t have any clatter issues though. I don`t notice any engine sound difference after switching. The engine does idle a little higher, and seems a little peppier. It used almost no oil before, and uses almost none now.
I`ve never done a UOA on this truck, and have the kit when I get 7,500 miles.