HI if you let me know what you wish to know and what model and year you have I will try to help you. Like a newer 4.7 motor? Certain motor can do odd things like drop valve seats. I can look for common problems with the model, year, and motor size.
The lower compression is usually related to valve problems. Often needing service. Also how much lower is the compression on that cylinder? Occasionally it can vary some below the normal and is part of added errors from the testing.
Hope this helps. If so please click accept. If not then please let me know and I will try to help!!
ASE Certified Technician
ASE