NOS

You should be 11's in the 1/4 with no problems. What mph did it run in the 1/8? Low 90's?

IMO, if it's not picking up any mph on the back half of the 1/4 you have issues somewhere else. Have you checked the fuel pressure going down the track? Find and fix what's wrong now. If it's leaning out now it may be a small issue, leaning out with N2O can cause a big issue.