Hi Louis , sorry for the late reply.
The problem could be the fuser.
What you need to do is print a page of 25% cyan , then magenta, then black.
If you can see the same band in each colour , that should be the fuser or maybe 2 BTR. Make sure the sheets you print out are A3 at least. Measure the band , point to point and tell me the distance in mm. Also create a paper profile and decrease the transfer rate to about 75%. That can reduce the banding .