Can of worms opened!!!
I was using Amsoil, but plan to switch to Shell Rotella T 5W40 synthetic diesel oil simply due to economics. I can buy it locally, no shipping or membership.
Others will chime in with their preferences. Really, most oils are quality today, some just need changed sooner than others.
'96 2500, CTD, 4X4 flatbed, Isspro gauges, Skyjacker D-25's, ThurenFab track bar, DSS, HD steering.
I like the john deere oil, it still is the CI-4 so it has plenty of zinc and phosphorus so you don't have to run additives like the cam manufacturers recommend with CJ oil. You can get it for around $13 a gallon.
Youre asking a broad question & requesting a specific answer. What oil to run depends on many things, such as the climate & conditions you live as well as the mods & uses of your truck. If this specific info is what you seek you need to give more details about your locale & truck. You really want to know what to run then do some oil analysis on different oils in your truck. Otherwise its all a matter of opinion. All name brand oils are basically equal. Run whats on sale & change it regularly.