Got it fixed, turned out to be a poorly constructed non-factory stack.
Instead of using a double walled steel pipe to connect to the 18" factory pipe that comes out of the top of the stove, someone had two individual sections (2' each) of thin sheet metal connected and running into the factory pipe, then had taken a single walled heavier stainless steel tube and slid it down over the sheet metal pieces ...then welded a spark mesh and cap on the top - so the sleeve/spark arrest/cap were all one solid welded piece - no way to clean the flue without entirely removing the sleeve, which meant breaking the sealant that was in place around the collar and sliding it completely off - big time pain in the arse!
Bottom line, the spark arrest and top 5% of the flue were 95% blocked up so the smoke had nowhere to go except back down the flue and was getting out around the seams of the assembled pieces of sheet metal.
I now have a single piece, double walled stainless steel stack (still 4') running from the 18" factory pipe up thru my roof ...and NO MORE spark arrest or cap. I'll just be mindful to keep a metal bucket on the pipe when it's not running.
And while I had the stove shut down, I went ahead and removed the fan cover so I could check the flapper (good shape and working) and grease the solenoid a bit. Fired it back up this afternoon and 99% of the smoke is exiting thru the flue as it should....which means a HAPPY WIFE tonight
Thanks for all the help y'all !!