There are several things that can cause your Cadillac Deville to have transmission problems. The most common transmission problems are worn transmission gears.
dirt in the speed snsor bad speedo head in the dash
1 or more out of balance tires
A bad resistor or a bad switch.
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.
door button stuck --bulbs? fuse.
The blower control module is defective.
The DeVille could have low transmission. Or the internal transmission bands or valves could have failed. The transmission will most likely need a rebuild.
7.5 with filter! Previous answer is incorrect, if you put in 8 with filter change you will be half quart over and cause problems!
uotside temp sensor in front of the radiator has gone bad