Direct Digital Synthesis - Super Sampling - Unknown Harmonics
I think that with a 250 MHz sampling clock, you should be able to generate a signal with a 125 MHz max frequency.
Also, what type of DDS do you use? Is it based on a table of sine/cosine or is it a CORDIC algorithm? It has an impact on precision.
Is the signal path from DDS to DAC ok? Do they work at the same sampling frequency?
If not, a resampling module should be used or correctly configured.