The "mod-motors" (4.6, 5.4, 6.8) are all generally fairly reliable, oil wise. They don't really care about what grade you use.
I would think any decent 5w-30 would do well; good overall choice that's hard to go wrong with; covers about any environment temps you'd ever see.
The failure the OP experienced likely had zilch to do with the lube used; it was a coincidental event.
There are plenty of examples of mod-motors running a million miles on many different grades of lubes. If your engine is going to fail, it's going to fail regardless of what's in the crankcase.
Here's just one example:
https://www.youtube.com/watch?v=yjRgiAOHm-E
I was interested in the history of this truck, so I called the service center seen in the video and spoke with the service manager (Total Tire).
https://total-tire.com/my_installers/map
Here's a synopsis of the overall history:
- first 5.4L engine ran 100k miles, had a catastrophic failure; replacement engine sourced from a salvage yard because the owner didn't want to wait on a reman or rebuild
- second engine 5.4L ran almost 1,000,000 miles; another failure; another engine sourced from a wrecked truck
- third engine 5.4L ran more than 1,000,000 miles; another failure; another salvage engine replaced it
- forth engine 5.4L ran another 1,000,000 miles; truck was totaled in a wreck
- vehicle replaced with another SD with 7.3L engine
I asked what oil is used to service the gas engines in this truck; only Havoline 10w-40 conventional oil, every 7-10k miles when the owner made it in during his delivery routes. Mod motors are not specd for that lube, but it seems to do fine. UOA macro data shows mod-motors really don't have an affinity for any one grade, although thicker oil does tend to cause issues with the VCT at times. BTW - you did read that right; the truck itself had over 3 million miles on it when totaled. Whereas the video covered the first million miles, the truck actually accumulated more than 3 million miles long after the video story was done by a local news agency.
My point? Well, if you want to credit the "thick" oil for the three engines that ran over a million miles, then you also have to blame it for the first failure of the OEM engine. Can't have it both ways ... Either the oil was the cause of engine failure, but also subsequent successes, or the more likely explanation is that the grade does not matter, and it was only a coincidence regarding the failures or successes.
And there's also this:
http://www.millionmilevan.com/
over 1M miles on Valvoline 10w-40. Mod-motor engine died; vehicle stopped. Longer OCIs (10k-20k miles). Did he use syns? Does it matter? If he didn't, you might want to blame the oil. If he did, why not blame the oil?
Lube grade selection RARELY has any affect on a mod-motor. Some other engine families may be finicky; not the mod-motors. If a mod-motor fails, it's due most often to a manufacturing issue or defect. It may fail in less than 100k miles, or it may roll to a million. If you were to use a grade so absurdly out of spec, it may cause an issue (say using a 10w-10, or a mono 50 grade). But about any decent and "normal" multi-grade oil (0w-20 up to 10w-40 grade and everything in between) pretty much returns the same expected engine wear rates, no matter what is selected.
You didn't mention UOAs, so I'm going to presume there were none. You have no idea if this was a chronic failure or acute; has it been degrading over time or just blew chunks all at once? I realize the failure seemed immediate to you, but the signs may have been present along the way but without UOAs you'll never know. Once opened up, you'll know more.
Most simply put ... the oil grade used didn't cause this engine to fail any more than it's going to assure the next one will last a million miles. And the same goes for base stocks; syns are not going to make it last a million miles any more than the dino example I showed above.
