Not sure why, but it from reading different threads it seem that with the 01's some can be read and some can't. My 01 F350 has the OBD II connector, but no sticker under the hood.
I think it gets a little confusing. I got my money back for the tester and was only out a few bucks for the program. The biggest thing was the time wasted trying to figure it out while my truck sat.

 

Test drove a buddy's Canyon with the 4 cylinder duramax..... and REALLY liked it. He is averaging ~55mpg in it.

Never been a fan of government motors, but that truck is awesome. When the doors fall off of old green, will probably be getting one of those.