8 x 3000 will make the motor draws over 35 amp. The one I have draws about 32 amp on 7 x 2000's. May be the 3000 Nimh can not supply the current. Are these 3000H or 3000HV nimh? Did you adjust the ESC so it is fully on ? I have 14 x 2000 and it goes very well. May be you need a higher rating ESC?

One last stupid question, is the rotor blades on correctly? The convex side faces forward and the concave side towards the back.

Brian