Don't confuse cam timing with ignition timing.
The timing belt controls cam timing. The ignition timing on the Zetec (Duratec too) is not adjustable.
Although a jumped timing belt can make the engine run poorly, I would look a lot of other places first. Timing belts don't usually jump, they usually break so that the engine quites running. At 75,000 miles it would be a good idea to replace the timing belt as preventative maintenance, but don't jump into it as the cure to your drivability problem. Anticipate the posibility of replacing the water pump at the same time.
To really pin this down, you need a fuel pressure gauge and an OBD II scanner so that you can see what is truly going on.
Some of the posibilities are:
Jumped timing belt
Plugged exhaust
Fuel starvation (plugged fuel filter, weak fuel pump)
Clogged injectors
Lack of ignition timing advance due to one of many sensors acting up or the PCM acting up. The sensors would usually set a CEL.
Badly worn spark plugs. (with this you should feel an actual miss though, at least under load)
Severly clogged air filter
Unfortunately, there are too many posibilities to pin it down without testing. It would not hurt to catch up on maintenance before you take it to a shop. You might get lucky and solve the problem.
What I would do at home myself before taking it to a shop if I had the tools and the skill would be to replace the fuel filter, replace the air filter, replace the air filter, clean the throttle body, add a can of injector cleaner to the tank (I prefer Techron or Red Line), and check the timing belt to see if it has jumped. If it has jumped, replace it.
Good luck with it.
