I have a 2002 ford ranger with the 2.3l and 5 speed.

Long story short, previous owner adjusted the time because he accidently got the motor out of time (he thought it had the belt, not the chain). So he had to take the intake, fuel rails, fan, throttle body, etc. Off to get to the valve cover to re-time it with the timing kit.
After it was put back together, it ran awful. I bought it, checked the time with the timing light and it was good. I replaced the spark plugs, and then realized he had forgotten to plug the camshaft positioning sensor back in. So I did, and that did the trick. From start to finish, the truck had those issues for about a year before I got it so it sat up for a little while. I have had it for 2 weeks now.

Now the problem...it idled great. But when I took it out for the test run, 1st gear shifted great, but at about 1700-2000 rpm (depending on the gear), it would almost seem to loose power, and then it would pick back up around 2400-2700 rpm like nothing had happend. You can sort of tell in 2Nd gear, but it is very noticeable in 3rd, 4th, and 5th. If i accelerate pretty slow, it doesnt happen. It only if i try to accelerate at a normal rate or if i am trying to get onto the interstate or pass someone. I ran some seafoam in it thinking maybe it just got gunked up from sitting for so long, but that only through an engine code saying my bank 3 was misfiring. So I replaced the spark plugs (again), wires, and then the coil pack (the coil pack is what fixed it) and that got the code to go away and for it to stop missing, but the problem still was the same. It would take off great, and then it would seem to almost pause, and then pick power back up again. It wasnt feeling like it isn't getting enough fuel, it just wouldnt hardly pick up speed. It almost feels like I am riding a 2 stroke dirt bike. The power band is ehat should be normal on the truck, and before I hit the power band is how it feels when the truck has its little pausing episode. It's that noticeable to me.
So I thought maybe the fuel filter or sensors need cleaned/replaced..so yesterday I replaced the fuel filter and cleaned every sensor around the top of the engine, including the MAF sensor and made sure all bolts were tight and gaskets were good.
I don't see and disconnected vaccume lines and none of them looked dry rotted. The only place air can get in that I see is the air filter box. The screws that hold the top half of the (stock) filter box are missing, so it is not sealed.
But I have no idea what to check next. My only other thoughts are the catalytic converter (which it doesn't act like it's stopped up) or the fuel pump pressure being off. Also, it does sound like a lifter ticking in the motor, but previous owner said he thinks it did that before all these problems.
Any thoughts? Also, right before I bought it, it sounded like the ujoint was squeaking (it rarely does it now) and now it has a crackling sound when accelerating at low-mid rpms coming from the middle or the back of the truck. It sounds similar to when you turn your hot vehicle off and the exhaust makes crackling noises sometimes.

 

I didn't see this mentioned but you may want to read up on the IMRC (Intake Manifold Runner Control). The intake manifold on 2001-2003 2.3L 4-cyls have flaps inside of them that open via vacuum solenoid somewhere around 2000 RPM I believe. This provides low end oomph then they transition open to allow upper RPM oomph. The common problem with the IMRC is a leaky vacuum hose(s) on the solenoid or actuator.

When I bought my truck I had this weird sound in the intake. Come to find out the IMRC actuator arm on the back of the intake next the the firewall has gotten disconnected somehow and the flaps were being sucked open (or closed not sure which) when they shouldn't be. Now that my IMRC is functioning correctly again I can now hear a really low tick coming from the flaps (the "IMRC tick"). These can loosen up on high mileage Duratec 2.3's and so I will be replacing my manifold soon.

Something else to look into is forscan.org. It's a great freeware analysis and scanning software for Fords.

 

Condensing 150 pages to one sentence:
Now the problem...it idled great. But when I took it out for the test run, 1st gear shifted great, but at about 1700-2000 rpm (depending on the gear), it would almost seem to loose power, and then it would pick back up around 2400-2700 rpm like nothing had happend.


In short, you have a 'flat spot' in your engine output. Apparently rpm dependent rather than speed or load.
If you hold the throttle steady, open a good bit, the will engine pull fine, and then start to act as if it wasn't receiving fuel, stutter, and hestitate, with NO throttle movement?
If so, that takes several things 'out of consideration', such as the MAF responding to airflow changes, the fuel pressure regulator goofing off on the job, the fuel filter being plugged/unplugged as demand changes, the fuel pump falling off in its delivery.
OTOH, the rpms are changing. The fuel flow is changing. The air flow is changing.

Get a fuel pressure gauge, and attach it, and check the pressure. The pressure regulator should vary the pressure based on throttle position(manifold vacuum). Check delivery volume, as your reported symptom is 'failure to respond when demand increases' more or less. You could also have gunk on a sock. The fuel pump pickup in the tank could have a couple years or more of gunk produced from decaying fuel left in the tank for years at a time which clogs the sock on the end of the pickup tube, and then un-clogs as the pump flow decreases, then clogs again... Delivery volume should indicate...
tom