I have a 2002 ranger 3.0L RWD and after about 20 minutes of driving, my O/D light will start flashing and the transmission will either lock me out of O/D (won't let me in) or FORCE me into O/D (even from 3rd it will go right to the highest gear available even if I'm still accelerating. Also from a stop I will have a REALLY hard shift into 2nd from 1st.

I also noticed that if I drive for a little while, my resting RPM's (which are normally around 900) are at 1500 until I tap the pedal.

Recently this the O/D light starts flashing earlier and earlier in the drive.

Any ideas? I tried posting a thread about this before but never got an answer

 

Here. Give this a watch. It may help shed a little light on a few things.

 

I just changed the fluid not a month ago and it looked fine when I did, I also replaced the filter (obviously) could a failing PCM relay do this or even the PCM itself?

 

Not likely.

The flashing OD light means that a TRANSMISSION trouble code or codes are stored in the PCM. To extract a transmission code, it requires a more powerful tool than a typical OBDII code reader so you might need professional help. Once you have the code, it should point you directly to the fault or at least narrow the possibilities.

 

Here's a cheap solution to getting the codes that pays for itself the first time you use it. Grab a laptop (you have one, right?) and head onto Ebay. Find an ELM327, OBDII to USB. I got mine from china for about 12 dollars. Order it and wait.

When it comes in, download and install 'Forscan'. Extra software shouldn't be required to make the ELM work with windows. Once you have it set up, turn the key to 'run' on the vehicle, plug in the OBDII connector to the OBDII port (found straight down from the steering column on the dash) and connect to the vehicle. It will read all the codes that the vehicle is giving you.