Do you have any UOAs to post?
Is your motivation cost savings?
IIRC, your driving conditions are “severe” as defined by the Owners Manual?
No UOAs to report. I did some a while back and things were fine but anymore I'm just going by what I feel is a good, conservative time and mileage frame for what most people running full synthetic and bypass systems do. Motivation? I was motivated primarily by wanting to cut down on the amount of supplies I had to haul down here (Mexico) to change the oil and filters. One full oil change every 20,000 is a lot less oil and filters than every 5000 as I was doing before. It does come out a little cheaper, too, which is a nice side benefit but not the primary motivation. Also, I like having a high quality oil in the motor and the Mobile One filters have a better filtration rating than the OEM Ford ones IIRC. I also like the cold weather starting ease that comes with the full synthetic oil as well. And, yes, according to the manual my conditions are "severe."
Early 99 F350 4X4 CC 7.3 Auto. A.R.E. Topper, bed carpet/bench inserts, Rhino grill guard, AIS w/sleeve, Fuel filler mod, GOS headlight harness, 02-04 Headlights, Rancho HD stabilizer, 06 Telescoping/heated mirrors with C-Btr Mirrors, Hella FF1000, Htr Bypass valve, front receiver hitch, Quadzilla XZT gauges, ITP Pre-pump/In-tank mods, Pioneer P5000UB w/XM radio, 4 Infinity Kappa 682.7cf, Fumoto valve, FIAMM Highway blaster horns, SS HPX, IDM mod, DP F5 (Stock,Drive-thru,60T,80E,120,80E-Mountain,1200), Walker BTM, RR, Dieselsite BRV, BTS Tranny (2nd one :-), 31 row tranny cooler, Bilstein shocks, Amsoil bypass oil filter, Stancor HD Glow Plug Relay, billet thermostat housing, front & rear parking cameras, Aux reverse lights, Heated Seats.
Security: CrimeGuard Alarm with remote notification, DIY jimmi-jammers, door cylinder locks and linkage removed, padlocked rear bench seat hinge, PCM, DIY "pitstop" switch.