PDE solve

Hi all, as part of the design of a catalytic combustor, I had completed a PDE system that governs the temperature distribution of air and ceramic as hot air flows through a honeycomb Ceramic cylinder. I am positive that the PDE system is right, however when plotting the result using MathCad, it doesn't look right, the plot is overshooting and not stable, the graph should be decaying exponentially. I found that by adjusting the xpts, and tpts ( the discretisation pts in PDEsolve) the graph tend to change but still haven't got the right results! my question would be, is there any relation between the Xpts and tpts to get the right answer?
I have attached summary of my work

Thanks !