Top quark pairs at the Tevatron are produced with an anomalously large forward-backward asymmetry. Discovering the source of this asymmetry is a major physics goal for analyses at the Tevatron and the LHC, because it is difficult to account for within the Standard Model, and may point the way towards new physics. We find that this asymmetry depends approximately linearly on the top quark pair mass and on the rapidity difference between the top and anti-top. We also observe an asymmetry when studying only the lepton in semi-leptonic top pair events which is consistent with the top pair asymmetry. Finally, we see an anomalously large linear term in the top quark pair differential cross section, which is sufficient to account for the asymmetry. These results may be indicative of undiscovered phenomena, or they may spur advances in Standard Model computations.