Do you have the high speed pulley on it ? Maybe 6'' size or something near that on chopper shaft, dual groove belt. And like mentioned if knives are worn they may not grab the material as well. Don't quite understand your reply posted above.
Are their flaps attached to the back of your chaffer to keep the material moving down into the chopper
Do you have that plastic deflecter mounted inside the machine above the chopper. Is the chopper flinging material back up inside your machine?
My first year with one, I installed a used one. Worked great, probably better than the guy I bought it from, there were 12 of the winged knives installed backwards. Noticed it before I installed it.
I also noticed on mine someone used a torch and cut the discharge off 1 1/2'' on the bottom to open it up more, not sure why or if it was nescessary.