Rock, I do believe that shortening or lard or butter is what is called a non-newtonian fluid which can have some rather strange propeties when it comes to viscosity. As for the Non-newtonian properties, see the list:
1. dilatant: viscosity increases at increased shear
2. pseudo-plastic: viscosity decreases at increased shear
3. rheopectic: viscosity increases at time rate of shear
4. thixotropic: viscosity decreases at time rate of shear
Now that I have thourghly confused the issue for you, the tables I've got don't list the medium you're asking about. My suggestion is to contact either Robbins & Meyers Moyno Pump division, they manufacture progressing cavity pumps with low shear properties, and have extensive experience in pumping non-newtonian fluids. Or you might try, Trans-America Delaval, Imo Pump Division they also have experience in progressing cavity pumps and non-newtonian fluids.
Good Luck!
saxon