Being nuts , I have to ask a nutty question.
"why would you shift heavy cargo whilst in flight?"
Also Tho it is common practice to trim in elevator for max speed -I never have been asked to "move to the rear to speed this thing up" --
The lift required for flying straight and level is dependent on the speed and weight --
Now then-- how much speed is to be gained --percentage wise --changing ONLY a moving CG --and retrimming (no weight change.)
Lets understand that CG was "close enough" to get the thing in the air ---
Has A-- the lift actually changed ?" B-- trim drag is reduced?
C ---something else - gremlins maybe?