New holland 660 bale sizer not working properly

I have 660 roller that we have owned since new in 1995. Starting last year I have been having problems getting a proper bale size. When I first start baling for the day it seems to work great but after a couple bales the bale command will start counting almost as soon as the tail gate shuts. Starting off at 30 all the way up to 66-70 for a full bale even if there is only a core in the bale chamber. While I am baling I have been putting the system in manual mode instead of auto and just keep an eye on the expansion cylinders to guess on the bale size. While I am baling I can shut the pto off and the bale command will display the proper size, once I re engage the pto the bale size will start climbing again. I have had newholland look at it twice. First Time they sent my baler computer off to be repaired and the second time they replace the potentiometer.

New holland 660 bale sizer not working properly