At present, 3dfim+ only allows polort <= 2 for historical reasons (3dfim+ dates back to about 1997, I think, and was one of the first programs Doug Ward wrote for me).
I will modify it to allow higher order baselines, using Legendre polynomials, like the new 3dDeconvolve, since at present 3dfim+ just uses the basis set {1,t,t^2,...}, which is not numerically stable.
The new version will be posted sometime this afternoon or evening. Look for an announcement here.