What to check??? Cruise Control won't set

[osbornsm]

Afternoon all,

I have a 2011 370z with sport package and 55k miles.
- The dealer will NOT cover the Cruise Control issue on the 60k warranty.

What sort of things should i be checking for to try and resolve this issue???

Info:
- On / Off cruise control function works
- No Check Engine Lights
- No flashing Cruise Control light
- "Set" feature will not maintain my speed
- I'm not trying to set cruise @ 100 or 15 mph
- Aftermarket Kenwood headunit has been installed for 30k miles
- No other electronic mods

Thoughts?!