I have found a solution for the difficulty I was having pulling five of my seven new Lionel 86' Boxcars.
ORIGINAL POST: Three of the cars are uncoupling while traveling on my minimum O-72 curves when pulling other cars. When I reverse the train to re-couple, the cars are jumping the track when pushing a string of cars.
SOLUTION: I heavily oiled the Kinematic plate and couplers with Labelle 107 Oil. After four days of running the 86' Boxcars, the metal Kinematic parts began to wear the rough edges on the plate and arms so they had less binding/drag when moving side to side.
Eventually I was able to reverse a train of eight cars at speed step 3.
The new 86' boxcars appear to be the same weight as previous cars. Running the cars to wear down rough edges on the plates and plate cover is the solution that worked for me. The excess oiling allowed me to get the cars started moving on the "wear-in" process. After four days of running the cars, you can remove the four screws holding the kinematic plate cover and look at the wear pattern caused by metal to metal contact. Paint will be scraped off the cover plate and metal coupler glide.
I now can run nineteen 86' Boxcars at "Speed Step 125" without uncoupling or derailments. The rough edges created during the metal stamping process have been worn down with use.
Sincerely, John Rowlen