Yes, fuel filter should be changed every 5 years or so.
I would get a Vacuum gauge(under $25) and see what kind of vacuum you have at idle.
Good read here on tests to do and what results mean: Technical Articles: Engine testing with a Vacuum Gauge - at Greg's Engine & Machine
Low vacuum at idle could be timing belt has stretched so time to replace it.
Raising RPMs to 2,500 and then hold it there while watching vacuum gauge, if it starts to drop then you have clogged exhaust.
Has the MPG started to go down recently?
Have you been able to check if there are any codes in the computer?
Some auto parts stores have OBDI readers, they will check codes for free, WRITE them down.
On a '94 you should be able to get any codes yourself using the "Check engine light"(MIL/CEL)
It will flash out any codes, current and in history.
Read here: Ford Ranger - Testing EEC-IV Equipped Engines
There are also videos on you tube that show what to do.