Won't start -Need help

[cdbrooke]

Need help.
Won't start sometimes. 2011 Backdraft 4.6L 3v Roush motor with supercharge.
Fuel pump initiates with key in the on position, clicking noise as start button is pressed (solenoid sounds like it is working), but motor won't turn over.
I replaced both battery and starter motor. Alternator works fine.
Mechanic thought it might be an excess heat problem with starter or kill switch (location).
Does anyone have any ideas. I can't believe this is the only Backdraft with an excess heat problem that affects starting the motor. If I go anywhere I cannot shut the motor off; might not start again.
Thank you for any assistance.