Loss/lack of power/acceleration

I have a 1987 Ford Ranger 4x4 2.9 Liter XLT truck, and it has 174,000 miles or so on it. The problem I am stumped with is this. The truck has lack of power or loss of acceleration, especially when attempting to go up a slight hill on a paved road.
It seems as if it just doesn't have the power it use to.
I have to shift down in fourth and floor it when goin up a hill, the truck slows down to 45 and has no acceleration whatsoever. So I am now in the process of trying to find a diagnosis and fix my problem. I started at the low cost items first and am working my way up to the more expensive ones. Here is what I have done so far. Replaced the spark plugs, wires and inspected the rotor and replaced the distributor cap. Replaced the clutch, pressure plate, throw out bearing and slave, and the pinion bearing. Also after reading the codes I replaced the MAP sensor, the EGR valve, the air filter, changed the engine oil and filter. Have punched out the catylitic convertor. Have checked the oxygen sensor, manual transmission fluid level, and have inspected both the axles and all of the brakes for resistance or dragging. Checked the Timing and it appears to be good. I also have replaced the in-tank fuel pump and the screen or sock, have replaced the canister fuel filter, replaced the in-line fuel pump, and replaced the in-line fuel filter, and replaced the fuel pressure regulator. I also have checked all of the fuses and have ran the test on my ignition coil and it checked out as good. I also have performed a Compression Test on the engine and all of the cylinders check out good around 175-180. I have done all this and still drive it down the road and it still hesitates to accelerate. I am now to the point where I think I am going to replace the EVP sensor and then I am going to replace all of the injectors. I recently read an article that said plugged injectors can cause the type of syptoms like I am having. If this doesn't work then it has to be the Throttle Position Sensor ot either the Mass Air Flow Sensor? Right? Or should I replace them before the injectors? I have worked a lot on Rangers (I've owned 4) but I have never had a problem like this and I am struggling to find the solution. My wife says if I keep going I will have replaced and rebuilt all of the engine parts before long. Do you have any ideas, as to what may solve my trucks lack of power problem? I am getting very discouraged.