The '94 4.0l should have an A4LD trans
Good read on it here:
http://www.therangerstation.com/tech_library/a4ld.shtml
Should have an electronic locking torque converter, do you feel it slipping?
Lack of power at higher RPMs/speed could be a few things, obvious first thing would be replacing the $10 fuel filter, I am sure that was done already.
A fuel pressure test would be helpful, you want approx. 35psi to be sustained at steady higher RPMs, fuel pump pressure might be fine at idle but flow is what comes into play at higher speeds.
Assuming new fuel filter, the fuel pump could be lacking sufficient flow or the screen filter in the fuel tank may be getting clogged up, so at higher speeds not enough volume of fuel can be pumped.
That's the getting enough fuel part.
On the upper intake is the TPS(throttle position sensor), when you press down on the gas pedal the the TPS tells the computer how far down you are pushing the pedal, if the TPS sends computer 1volt that means foot is off the gas pedal so idle fuel/air mix is needed.
If gas pedal is pushed to the floor the TPS sends computer 5volts and computer runs fuel/air mix for WOT(wide open throttle).
So 1volt to 5volt range is how the computer tells what is on your mind as far as speed/RPMs go.
Mechanically the throttle cable can stretch, so when you push gas pedal down to floor the throttle doesn't open all the way so computer only see 4volts, 3/4 throttle is all you will ever get.
Easy to check this, remove throttle linkage cover, have someone push gas pedal to floor(engine OFF), and then see if you can open throttle manually a little more.
If so, there is a way to shorten stretch throttle cable, look under the dash above gas pedal, you will see the cable end, lift up on gas pedal, you will see part of the bare cable exposed now, put a zapstrap/wiretie around bare cable part, so you are in effect shortening cable.
If cable is fine then TPS could be limited, it has 3 wires, 5volts, Ground and "voltage return".
The voltage return is what the computer sees for throttle position.
With key on engine off, use sewing pins to pierce wires and test voltage, usually center wire is the "voltage return"
With throttle closed it should show .8-.9volts, with throttle wide open it should show 4.6volts or higher.
MAF sensor tells computer how much air is coming into the engine, this is the main sensor for engine performance, the big kahuna, lol.
But easy to clean and test:
http://www.therangerstation.com/tech_library/CleanMAF.shtml
Since an engine uses more air than fuel(14 parts air to 1 part fuel) the air flow is very very important, make sure air filter is clean and it's air intake is clear, no "mouse house" or other restriction, sounds simple but seen air tubes blocked before.
And blocked air flow could be the whining noise you hear.
Is the whining sound only in gear, if you shift to Neutral and while coasting does the whining change with RPM or wheel speed?
High pitched whine can be the beginning of a wheel bearing going out.
If you rev engine in Park do you hear the whining?
If so, loosen serpentine belt(take it off tensioner), then spin each each pulley manually and listen for roughness or noise.
I just replaced idler and tensioner pulleys on my '94 4.0l because of a noise, I guess 20 years was their limit, nothing is built to last anymore, lol.
If nothing sounds off, start engine without belt and rev it to see if you can get the whine to come back, it is OK to run cold engine for a minute or two without water pump or alternator.
If you do get the whine then see if you can localize it, without the fan noise it should be easier.
If no whine then recheck pulleys, you got a bad one, just have to find it.
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