Hi, I have a 4.0L EL Falcon on gas/petrol.
The transmission had been playing up since I bought the car (330,000kms). When the engine is cold the transmission shifts like new, but once it reaches operating temperature, the revs flare up and the car dumps into 2nd, and does the same for 3rd.
I replaced the transmission last weekend, and it was fine for a few days, now it's doing exactly the same thing.

I've read on a few forums that it may be TPS or inhibitor switch related, but considering I just used the inhibitor switch that came on the replacement transmission, I'm leaning towards TPS.

Any other tips or advice would be great, cheers.

put fluid in it they slip and f**k up if its low

I've replaced the TPS and inhibitor switch, still no good.

Could it be related to the oil cooler? Blocked perhaps? I'm all out of ideas here.

Also, I used Dexron III to fill the trans, which apparently is fine as far as the recommendation of the bottle goes, but I've also read only to use 95LE or TQ95, not DX3. Could that be the problem?

best way to find out if its blocked is unhook the lines and run a compressor through and blow out the s**t, and as for fluid ring ford and ask them wich oil to use that's what I do but I always use whatever is cheap and never had a problem. Did you fill it till it was over flowing that's also what I do, easiest way is get a hose to a 600ml coke bottle feed it through where the shifter goes get someone to poor it in whilst you hold the hose in the box its a large alan key for the plug in the side.
if still not sure see a mechanic coz im not good with anything else to do with autos just throw in a manual and f&*&ck off the auto

It's the s5 shift solenoid, common on high mileage transmissions. Causes no issues if left. Low oil level will cause it to slip into neutral when cold or after a hard stop. Pull TPS when it shifts hard & you will see it changes completely differently as it overrides the s5.