After talking to a couple mechanics and having diagnostics run, I've decided to give this a shot. I have an 03 Ranger Edge, 3.0 motor, and 168,000 miles. I have this truck for nearly 3 years with nearly no trouble. However, recently it has been a "when it rain, it pours" kind of few months. I had trouble shifting originally from a plug wire contacting and causing a short when I cranked my truck. Changed plugs and wires, easy fix. I had some issue of running for a bit and was my coil pack. After 13 years, it needed an new one. Not a big deal. At this point my truck is having trouble shifting/not shifting at all when I get 70-75 mph at 3,000 rpms. If I am on flatter ground, I have no trouble shifting in order to pass or speed up. However, an incline causes my truck to run high 3000-3600 rpms without shifting. I cannot figure out why. My transmission fluid was recently changed out and gasket too. I have had consistent oil and filter changes. I had an 02 sensor go off for a while but that is now off. One mechanic did a deeper diagnostic revealing it was an idle air intake valve issue. I wanted to make sure this wasnt something else before I drop the money on the part and it not fix things. I also have a clean mass air intake, so that isnt a problem.

 

Welcome to the forum

Assuming an automatic transmission, 5R44E model on a 2003 3.0l Ranger.
Also assuming 2WD not 4x4.

And I think you mean you had trouble "Starting" because of a shorted wire, not "shifting"


The early 2000's Ranger did have a bad batch of coil packs, but the bad spark plug wire is probably what killed it, or it would have been replaced before 100k miles.

What does this mean?: "I had an 02 sensor go off for a while but that is now off"


So your Overdrive(OD) is not working you think, the 5R transmission also uses OD for 2nd gear, so when you have a chance see how many times it is shifting from stop to 60mph on flatter road.

5R is a 5 speed
1st, 2nd(1st + OD), 3rd, 4th, OD

So you should feel 4 shifts
1st to 2nd, 2nd to 3rd, 3rd to 4th, 4th to OD

5R is also fully controlled by the engine computer(PCM)
And this control is based on what "gear" you select on shifter.
Ford trucks, including Rangers, had issues with their column shifters getting loose
On the transmission is a Digital Range sensor, it "tells" the computer what "gear" you have selected, Drive or OverDrive
If you select Drive then computer stops shifting when you get to 4th gear, people use this when pulling a trailer or hauling a load, when shifting to OverDrive would be hard on the transmission and engine.
So could be you are just selecting the wrong "gear"



IAC(idle air control) valve won't cause any issue with shifting
IAC Valve used use for starting engine, opens all the way, and is then used to set idle RPMs, 1,100 cold and then 750 warmed up