Can anybody explain or give me clues to why the kinetic trans effect and the spectrochemical series do not have exact correlations? I know it has something to do with filled p orbitals, but I cannot figure it out.
The spectrochemical series has to do with the strength of bonding between a metal center and its ligands, while the trans effect has to do with the stability of pentacoordinate transition states in ligand substitution of square planar complexes. It's not clear to me why you think they would be exactly correlated in the first place. Pi-acidity is important in both cases, but for somewhat different reasons.