2007 D40 auto transmission problem

Hi all
I've got a problem with my 2007 Spanish built D40 auto. Had a slow drive down the freeway this afternoon.
I have no 'strong' drive thru the auto. The car moves very slowly off the mark and feels like you are trying to pull a dead weight behind you. The engine doesn't feel the same load. I can get up to about 80kph slowly but engine is doing 3000rpm but there is no power or torque thru the gearbox. The engine revs quite freely at this speed but doesn't accelerate. It will hold 80kph up a hill but i have to hold the rpm's at around 3000 or it will rev out. It sought of feels like when you are parked and you just rev the engine. It does however seem to be ok in reverse.
I could not find any leaks from the auto and the fluid level was ok (i also had it check about 5000km ago).
This problem occurred without any warning and made no noises. I was on a dirt road in 2wd with another car when we stopped to talk side by side (so only coming to a complete stop for a few seconds and without changing the gear shift) and when i went to take off i had no 'strong' drive.
Could anyone have any suggestions as to what might be happening?
I'll be on the phone tomorrow to the mechanic to see what he can do.

Thanks

Additional info.
200k on the clock
Trans fluid changed at 150k
auto temps normal. (I have a auto trans temp gauge.)
Engine temps normal.
Boost was normal. (readings via Scanguage)
I went for another drive after being stopped for an hour or so and heard a very faint noise like a belt or chain free spinning. (not a fan belt or timing chain). Is there such things inside the transmission?

It could either be the transmission in limp mode or something inside the transmission is causing it to be stuck in probably 3rd gear. I'd try removing the negative battery terminal for a few minutes to reset the computer first, if you haven't already. If no luck with that it might be worth having the mechanic drop the pan and see if there are any metal shavings in there, indication internal failure of something.

I never thought of a reset. I'll let the mechanic put his scan tool on it first (he is good to me so it shouldn't cost much. A few beers is the going rate i think.) to see if there are any codes, then we can reset.
Thanks

No worries. Hopefully it's just a sensor that's lost the plot and a reset fixes it...

Update
Been on the phone with Wholesale Automatic Transmission (great to deal with over the phone) this morning and the guy seems to think the transmission is in a safe mode. Going off what I told him he said it will be in 3rd gear and scanning it will bring up a code to let me know what the problem is. I should have the code later today and I will post up what it was.

Update
Code was P1757, which relates to FR-B solenoid circuit.
I think FR-B mans front right brake solenoid.
That was all they could tell me today. I'll find out more tomorrow.
After trolling thru a couple of other forums, as well as this one, apparently most solutions to this code is to replace the valve body.
Could anyone shed some light?
Thanks

Update
Got the dreaded phone call. The computer inside the tranny has died.
$1500 and a 2 week wait.
Has this happened to anyone before?

Most of the D40 auto issues in the past were related to the torque converter and specifically the TCC which would rapidly engage/disengage over 75km/h and cause a vibration. Problems with the TCM are rare - at least, there aren't many reported here. Doesn't mean they don't happen - but in reality there's only a small proportion of Navara owners that jump in here.

If you go the Wholesale Automatics path though, you will be pleasantly surprised. I've heard from a couple of people who have upgraded their valve body and discovered a more spritely, powerful gearbox. Couple it with a lower stall speed torque converter and you will have more power available at lower engine RPM which will result in fuel savings.

Obviously other options include second-hand valve bodies/TCMs (or entire box). If the box gets reconditioned with a new valve body I think you'd end up with a known quantity that performs much better, compared to the unknown of a second-hand box.

The word I got from the specialist is that this is a common problem for the transmission. They use the same tranny in the pathfinder and the Nissan 350Z. The shop that is fixing it does a lot of the local dealership work, so he knows quite a bit about them.
As for Wholesale Automatics, I would love to upgrade the valve body and torque converter but at this stage they are still fine and funds are just not available for that if it's not absolutely necessary.
I'm putting the upgrades on the wish list (I think I better start another page for that list).
Thanks for the feedback and i'll post if anything changes.

Update
All is good in my world again. Got the car back with a repaired TCM and thought all was good until leaving the Mechanics. The noise i had heard which i thought was coming from the auto was still there. A quick u-turn and i was back in my mechanics driveway. He said that noise was the turbo and had nothing to do with the auto. As i needed the car, i thought i could investigate myself at home. I found that the dump pipe had no nuts holding it on. They had come off for no apparent reason and the noise was the turbo spooling up and leaking thru the gasket. A quick search on this forum, and this has happened to someone else. 3 nights in the shed later and a new gasket and nuts, and i'm back in business.
In summary, all D40 owners should check their nuts on the dump pipe. It's not easy to see due to the heat shield but you should be able to see if they are there (tight or not).
Everyone check your nuts!!

P.S. The auto is now fine and the report on the condition of the oil and other parts was good. No sign of any other problems. The TCM had just decided it didn't want to play ball any more.

Excellent news, and yes that dump pipe issue has happened to me as well (loose, not completely undone). Makes a strange sound, I thought it was my idler pulley for the alternator belt, but after spritzing that nicely and still hearing the noise, I was preparing myself for an alternator replacement ... until the loose nuts were discovered. The gasket was acting like a reed in a woodwind instrument!

Anybody can tell me what scanner can we buy for diagnostic and reset of codes , panel lites such as srs light blinking.NAVARA D40 2008 ENGINE. . Please reply . Thank you

If your airbag light is blinking, try following the steps in this post.

For reading and resetting codes, I use a $5 bluetooth OBD adapter and free software from the Google Play Store (Android phone).