Brushless Stampede ???

Well it doesn't really surprise me that it isn't what you expected. I felt the same way once I got my 8s running. Now my 5.5 did surprise me though. I think my 5.5 has more top end and mid range than my 8s. I had my 8s geared 17/84 and the motor was smoking hot. I gear it 15/84 now.

But I do think once you gear up you'll see a big improvement. I geared my 4200 17/81 and 19/84. It did really well and the top end was pretty fast. Also, if you get a 8cell you'll see it really open up from what I understand. Good luck.