Never had a gehl, so this is a long shot. Our NH900 with aftermarket processor started plugging one year.  Pulled our hair out.  After trying about everything, and unplugging it for maybe the 15th time, I was sitting under it at night with a flashlight, and noticed that the deflector plate that follows the knives up to the processor had come loose about 1/8 inch.  Two bolts held it in.  That was all it took for the flow to not hit the space between the rolls.  Tightened two bolts and it never happened again.