The EcoColors Ash Series can cover gray easily.It sounds as though you have porous hair, since the virgin hair lifted easily. Resistant grays need a 45 minute processing time using equal parts color to developer. Since you have a semi color on your hair, this hair will behave with totally different results than virgin hair. Trying the Medium Ash Brown may be an answer for you with a 45 min processing time. (only on new growth). DO A TEST STRAND!!
It's better to be safe than have a haircolor you did not intend to have.
As far as fadage goes, what shampoos and conditioners are you using?Alkaline shampoos or shampoos with tea tree may encourage fadage. Porous hair in general fades more easily than non porous hair. Try a direct deposit color shampoo to keep faded ends intact.