I can't say this post will help. But to me it sounds like it fighting with itself on if it wants to downshift or not and thus you feel what you feel.
I've always just taken my foot off the gas and put it back on when going up a long hill, normally unlocks the torque converter all is good again. I've never had it happen at steady speed on the freeway though.
The plug gap is kinda small for those mods, shouldnt be a real issue I wouldnt think. A .050 gap is more typical to run.
Perhaps cleaning the throttle body and MAF sensor and unplugging the battery for a while to reset it and the "TAPS". (aka how the transmission learns, adjust to the way you drive)