1.) Flash directly to this file:
http://tomato.groov.pl/download/K26RT-N/build5x-132-EN/Linksys%20E-series/tomato-E2500-NVRAM60K-1.28.RT-N5x-MIPSR2-132-Max.zip
*I was never able to get the larger "Mega" file to work, at least not initially so I recommend the file above.
To enable 5ghz I had to do the "Clear NVRAM" Option before it was shown.
2.) Or if you don't need 5ghz (most devices do not support it and cannot........