Torque Converter Shudder

[themixerdoc]

Again new here, and no Infiniti/Nissan experience so help is truly appreciated
Just took my new (to me) 1998 QX4 on a fairly long drive for first time. (about 25 miles each way mostly highway/country roads).
Nice ride overall quiet and smooth BUT on way home I was coming down an exit ramp from a 65 mph highway. At about 45 MPH when lightly accelerating the torque converter gave a noticeable shudder. Between this now and discovering the strut tower recall and the damage I could see on my vehicle I am questioning the sanity of my purchase
Some background information. The vehicle has 115k original miles and been quite well maintained. Oddly in looking through the maintenance records I see the transfer case and differential fluids were changed but not the transmission. The fluid while not red anymore does not smell burned but is DEFINITELY in need of a change.
Is this a common issue on this trans when fluid goes too far beyond service life? Would Mobil 1 be a good choice here for a flush/fill? I also see Valvoline has a synthetic product that meets Dexron III spec. I am assuming Dex III type would work fine in this trans or should I use a different fluid.
Would truly appreciate help on this, and hope I did not buy a nightmare vehicle

[4xq]

Old fluid can cause shudder on any vehicle.

The Mobil 1 fluid is very good, but has gotten very pricey. Valvoline Maxlife has a good reputation, and I would not hesitate to use it at all. A gallon can be had for under 20 dollars.

Look at the Pathfinder / QX4 General Information and FAQ thread up above - the Dexron III spec is ok in these.

Hope that helps!

[Buzzman]

With 115K miles on the clock, you should really check and find out if the timing belt has been replaced.
It should be done at 100K miles.
If it hasn't been done, then you are driving a ticking time bomb

Edit: Just read your other thread on the running boards and you answered my question re: timing belt.
I have a 2002 with the 3.5 engine (Timing chain. Never needs replacing), so I don't know enough about your engine to give you much advice.
There are lots of guys on here who should be able to chime in with some tips.

[themixerdoc]

Thank you both for the help. I also understand there is no serviceable filter for the trans so it is a drain refill type correct? If so I plan on doing multiple drain fills until the fluid is all as fresh as I can make it than.
I did a t/belt on my Camry and did not relish the experience. But, that is a sideways engine. Any advice for DIY on the Infinity? It looks like the radiator needs to come out. Is the universal anti freeze a good product to use? So no issues on my Camry but wonder on the Infiniti.

[themixerdoc]

Just an update to this. I decided to do a pan drop since this was first trans service at 115k miles. I found Valvoline makes a synthetic Matic D fluid so I got 3 gallons at Advanced. Price was not bad. About $24 per. The real hitch was finding a trans filter kit with proper gasket. That became a 1.5 day quest!
Anyway I finally got new screen and gasket installed. magnet did not have much "hair" on it. Filled it up and ran it through the gears on stands. Dropped the fluid that was in it and filled again with another gallon of fresh.
Results are very good. Oil now looks clean and nice and pink (not dirty brown) and no more shudder. Note original was not burnt just looked old but did not smell.
I am going to drive it for a while and drop it once more after I get the recalls done. Since I still have another gallon here anyway. Than I think trans should be good to go for a good while.
I just wish this forum was a little more "active". My running board question has not been given any consideration. Also going to post to see if anyone has a source for patch panels for the rear quarters. This thing is so mint otherwise I would like to invest a little time and $$$$ to keep it that way