I believe that we have a FRA connection thread on either the LH or the Germany forum which may help.
I am a frequent FRA connecter but not to US bound flights, and as an EU citizen I think that I connect a little quicker ie there seems to never be a wait for our passport control but I often see a wait for non-EU.
Having said that, I like to give myself at least a 2 hr connection time in FRA whenever possible. Invariably my longhaul LH flights have bus deplaning.
Honestly, I don't have much advice other than to check out the FRA connection thread.
http://www.flyertalk.com/forum/showthread.php?t=712844