  We study a generalization of the Kibble-Slepian (KS) expansion formula in 3
dimensions. The generalization is obtained by replacing the Hermite polynomials
by the q-Hermite ones. If such a replacement would lead to non-negativity for
all allowed values of parameters and for all values of variables ranging over
certain Cartesian product of compact intervals then we would deal with a
generalization of the 3 dimensional Normal distribution. We show that this is
not the case. We indicate some values of the parameters and some compact set in
R^{3} of positive measure, such that the values of the extension of KS formula
are on this set negative. Nevertheless we indicate other applications of so
generalized KS formula. Namely we use it to sum certain kernels built of the
Al-Salam-Chihara polynomials for the cases that were not considered by other
authors. One of such kernels sums up to the Askey-Wilson density disclosing its
new, interesting properties. In particular we are able to obtain a
generalization of the 2 dimensional Poisson-Mehler formula. As a corollary we
indicate some new interesting properties of the Askey-Wilson polynomials with
complex parameters. We also pose several open questions.
