this cub doesnt slow down,
I would say it is nose heavy. Regardless of where you have the CG now, add a little tail weight.
An easy test is to see if it will spin. Get lots (LOTS) of altitude, nose it up at a steep angle, chop the throttle, and just as it stalls, bring both sticks to the lower right-hand corners (Full Low Throttle, Full Right Rudder, Full Right Aileron, Full Up Elevator). If it spins really good, the CG is probably pretty close, but if it just spirals down, it is Nose Heavy.
If that's the case, shift or add some weight to the tail, and you'll see her settle in nicely.