'87 Thunderbird Shifting (Automatic)

My 87 Thunderbird has been shifting really late lately. Her first shift will be at around 38-40 MPH. It used to be around 20 MPH. I do have a led foot but I dont think that has anything to do with it. Why is she shifting so late now?

It is possible it is just low on fluid. This is also a symptom of a plugged filter, a weak pump, bad modulator or incorrectly adjusted linkage. Start by changing the fluid and filter. You have nothing to lose here, as this is just routine maintenance. Then,check the line going to the shift modulator. If the problem persists, I would seek the help of a competent transmission shop.