How difficult is it to replace the fuel filter or fuel pump on a 89 Plymouth Sundance?

Fuel filters are easy. Fuel pumps are hard. Buy an after market maintenance manual for your car. Read and understand the instructions for each of these thoroughly before starting. Use brass tools (fuel pump), they don't make sparks.

Additional: Fuel pumps aren't really too hard. Definately get a manual, but it's very do-able. You'll need to jack the car's front end up to tip the gas back in the tank, release the bolts on the pump, and pull it out. Keep a bucket handy to catch fuel spills, and make sure you release the pressure on the fuel line, if there is any. (Especially on a turbo, because it will be very pressurized!) Despite being in the tank, it's a fairly easy operation.