Replaced my transmission on the cheap with a boneyard unit. Shifts fine at very light throttle and when I jump on it. But with intermediate throttle opening (3500 rpm shifts) it does a slip-bang into 3rd gear and, rarely, into 4th. It has a parts guarantee, but for $700 labor I want to see if there may be a simpler fix before taking it back. Any insight welcomed. Thanks!

 

You will have the 5R55E 5-speed, in a 4.0l SOHC Ranger in 2003

5R55E doesn't actually have a "2nd" gear, Ford added 2nd to a 4R55E(4-speed) by engaging OverDrive while still in 1st gear, this made a smoother transition from the high ratio 1st and low ratio 2nd in the 4R, and gave them a 5-speed from a 4-speed, very clever

So the hard shift to 3rd could be a few things, i.e. overdrive system or 3rd system

Common issue on the 4R and 5R were the valve body gaskets, they would leak so internal pressure would be lower causing any number of issues since all automatics run on pressure.

I can't say "this is the problem", I doubt anyone can, even a trans specialist.
Automatics are not that complicated but..........the internal systems are interdependent so any one symptom can be be caused by a number of things.

It could be the torque converter lock up, TCC, it locks and unlocks torque converter so you can stop "in gear" and so shifting is not bang bang.

 

Well, as old Dad said, "Ya gets what ya pays for". I read elsewhere about the vb gaskets; also something about the EPT. Both involve shop time and at least a gallon of fluid. It's not absolutely awful, so with a six month parts guarantee I'm inclined to wait it out. If it pukes, I'm just out the labor.
Something just occurred to me after re-reading your description of the 5R552: If you toggle the OD off, will it still shift into "2nd"? Seems to

 

5th gear(OD) is Driver controlled, but not 2nd OD
1st
1st with OD on for 2nd
3rd
4th
5th OD, can be turned off by driver

The 5R55E shift solenoids are mentioned here: http://www.atraonline.com/gears/2006...2006-01_77.pdf
SS3 is the OD solenoid, it is active in 2nd and 5th


Probably EPC(electronic pressure control) solenoid, yes that can lower overall pressure in the system if is is leaking or intermittent, there would be transmission codes if its an electrical fault

 

Oops, I meant EPC. Forgot to mention no codes being thrown, but I'll do a real time scan to be sure

 

If no codes then you have a mechanical issue and/or internal leaks