I just had my 2010 F350 (9k miles) into the dealer last week for the exact same irritating issue which you describe. They test drove and inspected it and told me the same thing: "within spec". They also told me that there was NO adjustment possible.
In late July (a month after that June post above) I was down in Henderson NV and the play in my steering kept getting worse and more noticeable on the 750+ mile drive down there, so I took my truck into Ford Country in Henderson NV to check the steering out again.
This time I was able to go for a drive with the SM and he agreed that my truck had "unacceptable" play. He called Ford and they suggested a one-time 1/8 turn adjustment to the steering box done "exactly per instructions" so he called me back in to do it. I left it overnight, and they tried that first thing in the morning.
I had been quite insistant that this problem needed to be completely resolved this time as it was a severe safety issue for me and I didn't want to drive back home another 750+ miles wandering all over the road. Because of 1) my insistance, 2) the SM's agreement that it was a very *real* problem, and 3) I had asked Cory to get Ford involved ... the SM made the call that the adjustment wasn't enough and they *replaced* the steering box under warranty. MUCH better. My thanks to all involved.
The regional manager of Ford Customer Sevice had gotten immediately involved by phone/email (very nice guy, thanks!) thanks to Cory, but I think that the Henderson SM was really on my side this time (unlike the SM in Idaho). Plus it's easier to diagnose the problem with flat even roads, unlike all our capped and bumpy roads up here in East Idaho.
Anyway: Ford has replaced at least one steering box on a 2010 F350 under warranty due to excessive wandering on the road (and I'm damned happy that they did). BTW: It really helps to have the SM personally/fully understand the issue.
F350 SRW 6.4L 3.55 CrewCab FX4 SB KingRanch - built Jan 2010 - bought new Dec 2010
"You can set my truck on fire, roll it down the hill, and I still wouldn't trade it for a Coupe d'Ville."
Rant: Do you know what you actually pumped into your tank on last fill-up?
(cetane level, fuel quality, water, etc)
Notice: Anything that I or anyone else writes about my vehicle on this, or any other, website pertaining to modifications or alterations, is only for discussion purposes and/or to gain acceptance from my peers, and may not actually represent anything existing on my truck, and thus, can not and should not be held against me in any issues, i.e. warranty claims, whatsoever that may arise for any cause.