Why is the MAX2754 VCO output frequency changing from what is expected?

The most common fix for this type of problem is to check the voltage on the TUNE input pin. If you're using an external voltage source or resistive divider network to generate your TUNE voltage then there is a chance that noise or hot resistors will affect the input voltage and therefore the output frequency. If the resistors are getting too hot try using larger valued ones to alleviate the power dissipation.