Well the 2.3l doesn't have alot of power but I assume you know this and the current lack of acceleration is something new since you have had this vehicle when it was accelerating better.
First is to eliminate the obvious, do a roll test, flat ground let vehicle roll, making sure there is no drag from brakes sticking or transmission(roll in 1st gear with clutch pedal in).
Second, REV the engine, is it quick in responding to gas pedal input, or does it hesitate.
Next look at the drivers door label, get your axle code, read here: Ford 7.5 & 8.8 Inch Axle Tag & Door Codes
3.73 ratio is the usual
3.55 ratio and lower has slower acceleration but better MPG on highway, these lower ratios were popular with 2.3l since buyers wanted best MPG vs power or they would get 4.0l.
4.10 ratio and up has better acceleration but less MPG on highway.
Get a Vacuum gauge($25) and check engine vacuum at idle, expected is about 20, good read here on tests using vacuum gauge: http://www.gregsengine.com/using-a-vacuum-gauge.html
Vacuum gauge is one of the best tools for testing any gasoline engine, doesn't matter how many electronic/sensors and dodads they add to an engine, lol, it is still basically an air pump, so air in and air out can tell you alot.