said by a1computers:
DD-WRT doesn't look promising for E4200, probably try updating Linksys firmware first
I agree that the Linksys update if there is one for your unit is a good possibility to try or trying the alternate to DD-WRT, Tomato firmware.
tomato-E4200USB-NVRAM60K-1.28.0493MIPSR2-Toastman-RT-N-Ext which appears to be specific to your model. You might want to start reading at this link »www.linksysinfo.org/index.php?th ··· s.35865/
and see if Tomato is something you want to try.