tiazzz,
If you're coming from an 'audio only' machine, I can certainly understand the frustration.
While some describe the CTX as a 'turn-on-and-go' machine, I found it to require quite a bit of time and familiarization before the light bulb in my head finally turned on.

And it's even more of a 'display info' machine than it's cousin, the E-trac.
One thing to make sure of, is that you double-check your hole after finding the iron. The CTX can 'co-locate' multiple items in the FC mode, and it's tempting to fill the hole and walk away after finding iron.
Check that hole again! Sometimes, you've just cleaned the trash out and left a coin for the next guy. (Even when you do find a coin, check that hole again!)
The only thing you've said that concerns me is your depth numbers...4"-5" is awfully shallow. What kind of ground are you working? and/or What part of the country are you in?
Severely mineralized soils will limit detection depth, but I'm in Colorado (pretty badly mineralized) and I still get 7"-9" regularly. Sometimes deeper, depending on the ground moisture.
Also, how is the EMI/RFI 'electrical noise' in your hunt areas? You want to be sure to always do a 'noise cancel' before hunting, especially near transformers and/or power lines. That can affect depth quite a bit.
The only other thing I might suggest, is that you give Minelab service a call, and mention the depth issue. They might have you send it in for a 'check-up'...that's the only real way to see if the machine is working properly.
Good luck,
mike