A bad resistor or a bad switch.
The blower control module is defective.
There are several things that can cause your Cadillac Deville to have transmission problems. The most common transmission problems are worn transmission gears.
Absolutely
My 1998 Deville Concours had a blown blower motor for the heater/ac unit. I had to replace it because it stopped working likely due to age (replaced in 2008) and it was filthy when I took it out. Hard to do this by yourself but it can be done if you remove the obvious things in your way underneath the hood. Good luck! The blower motor fans cost around $130 ish.
dirt in the speed snsor bad speedo head in the dash
Heater coil
1 or more out of balance tires
One reason a 1998 Cadillac Deville would cut off while driving could be the fuel pump or the car is out of fuel. Another reason could be the spark plugs.
If the pedal is stuck down, no vacuum to the release diaphragm on the pedal
check radiator for small leaks or cooling lines which would most definitely cause it 2 steam when running after awhile
door button stuck --bulbs? fuse.
Check the A/C fuse, that's what happened on my '85.