Go Rebels, seems like the 3d's are not good in iron, so I use a different detector for nail infested spots. Not to say you can't find old coins among the nails, but the 3d dosen't seperate well. Darn deep though.
After you GB the machine turn the GB knob a hair (real hair) clockwise and many of the falses turn to iron grunts. I never turn down the sens. Once you go below 4.5 ish it looses depth. Disc always on zero. This is for hunting old coins.
If this winter turns into a "Winter" we're use to, I'm sending the 3d to Tom D for a tune up. That may reduce some of the falsing in iron. I have noticed much of the falsing is from iron just outside the coil and as you said it slows you down to analize. When that happens, if I can PP the target, then go over it from different angles. If it high tones 360 degrees I dig it. If it grunts in a couple small sweeps, it is usually iron. I have dug hundreds of targets to realize this.
After the tune up, I may have to change strategies.