How to get from IAS in MPH to KCAS using POH graph of best TAS/GPH?
Several questions here that need answers;
V(L/D max) is best glide speed.  Look it up under emergency procedures in the POH.
Airspeeds:
TAS is EAS corrected for temperature.
EAS is CAS corrected for compressibility.
CAS is IAS corrected for installation errors.  

IAS/CAS correction is available from the POH.
Pilots can use an E6-B flight computer to convert between CAS, EAS, and TAS.  

For more on this topic; here's a good link