I don't think I would go with SeaFoam in the oil. NAPA carries a product for use in cars before you change the oil that is supposed to knock the crud loose so it all flushes out with the oil. You drain a quart or so and put this stuff in and run for a while. The NAPA parts guy swears by it. It is on the shelf by the oil in Burlington, WI
On that note, I have also heard bad things about doing this (with switching back and for between detergent and non-detergent oil) bc it will knock crud loose and plug up oil passages.
If you want to run it like that, I would only put in about a quarter bottle and NOT RUN IT FOR A LONG TIME. SeaFoam is mostly petroleum distillate (READ: BrakeKleen, Lighter Fluid, etc) which are a strong solvent. I could see cleaning stuff, but also cleaning stuff too good that it doesn't get oil.
I am with Jim, I run Rottella T syn 15w40 (?) in my Powerstroke and it is great. Easier starts esp in winter and pretty quite (for a Powerstroke).