  We present the results of the first complete calculation of the tree-level
$2\to 2$ high-energy scattering amplitudes of the longitudinal modes of massive
spin-2 Kaluza-Klein states, both in the case where the internal space is a
torus and in the Randall-Sundrum model where the internal space has constant
negative curvature. While individual contributions to this amplitude grow as
${\cal O}(s^5$), we demonstrate explicitly that intricate cancellations occur
between different contributions, reducing the growth to ${\cal O}(s)$, a slower
rate of growth than previously argued in the literature. These cancellations
require subtle relationships between the masses of the Kaluza-Klein states and
their interactions, and reflect the underlying higher-dimensional
diffeomorphism invariance. Our results provide fresh perspective on the range
of validity of (effective) field theories involving massive spin-2 KK
particles, with significant implications for the theory and phenomenology of
these states.
