My friend got his 3.5 tremor tuned and he literally drives it like a lifted mustang. I drove that thing before and I still feel vibration but less noticeable, but he uses shell 93 only.
Honestly, this issue is pretty common for 3.5 EB. I can always feel a "slight shake" at idle even if I switch to 93 or even 94(petro Canada). Now I'm running 91 octane and everything is good except the slight shake at idle.
3.5 ecoboost here, I'd say I love this engine except some slight idle vibration at red lights. My friends own 5.0 2.7 and 3.3 even 3.5 powerboost. We've talked so much on this topic and I'd recommend you 2.7 ecoboost. That one doesn't have much power but true reliable.
No worries I think we all have the same problem here. I can't update successfully, too. I've tried over 5 times doing this and now I ignore this update. I believe the next update would be a successful one.