Hi Matt
Not sure what the thickness limitation is for this material plasma sprayed, but 0.050" on an internal diameter could be pushing it.
Pre-heat temp around 200 Deg C sound good, but is this a thoroughly evenly soaked temperature or perhaps less even obtained by a couple of passes of the gun?
Control of substrate temperature again sounds good, but I would try to concentrate or localise cooling on the hotter parts of the coating, rather than the outside of the substrate. Heat removal from freshly laid coating will be far more effective than removing heat after its soaked through the part. Ideally, a situation where the outside of the part maintains the initial preheat temperature at a constant value throughout the process, without the need of any extra cooling on the outside.
I suspect you are limited on selection of speeds and feeds by your handling equipment. If your coating deposit per pass is heavy, this certainly will not help the situation. If you can't reduce deposit thickness per pass by adjusting speeds and feeds, consider taking a little more time to spray the part using lower spray rate parameters.
Hope that helps and good luck