Hello there Ozpom:
Welcome to the Benzworld forums.
Lots of great fellow MB owners here to help out....some Indy techs / shop owners - MB dealer Techs from time to time, too !
I have a similar suv, our 2002 ML500, bought 'new to us' in Houston just a year ago, with 102k miles on the clock.
Truck was in immaculate shape, no sign of abuse, but not much in the way of maintenance records, either.
So i had to ask a lot around here, read the manual, google things, etc.
We already had our beloved E320 wagon, MY 2000, that has a similar themed V-6, very close to the 5.0l V-8 in the ML500, so a lot of maintenance & fixes are similar or identical on both rigs. (A decent argument, to me, for having both in our garage.)
FYI, the code for the engines is V-6: M112 V-8: M113
These both share the same basic tranny, the strong & reliable 722.6 Mercedes 5 speed Auto.
This tranny is AKA the '5-Gtronic' or the NAG1 - 5AW580 (the latter # being strength in Torque, Ft/lb), so the one in our e320 is actually a 5AW330 (if memory serves), for the lesser output of the V-6.
See here:
https://en.wikipedia.org/wiki/Mercedes-Benz_5G-Tronic_transmission
and here:
Good Advice For Owners Of A 5G-TRONIC Automatic Transmission Equipped Vehicle
So, there is a lot of strength in the drivetrains and as you've found out, yes you can tow.
Of course you need to have a proper tow set up in terms of MB or compatible hitch.
I'm curious if you used an Equalizing, load-levelling type hitch on your 2500KG tow adventure ?
I've only towed about 3000#, just last week in fact. The ML did great, power wise, and I just used a basic 2" ball, no load leveling bars at all.
(My only negative was the worn out shocks - new ones on the way - but it made me have to check my speed on the rougher surfaces as too much bouncing was very uncomfortable.)
Btw, on fluids:
Check and 10-4 on the sticking to the spec 236.10 ATF.
So much so that I don't thing the later fluids that meet 236.12 or 14 are as appropriate as our trannies weren't made for the ultra slippery later fluids that were made for the later 7 or 9 speed units.
Problem is that dealers tend to stock the newer fluids & not the older ones, so you have to go to extra work to find them. Extra cost too, sometimes.
I did my research & found a creative way around this, fyi.
The Chrysler factor spec for this same Tranny is ATF+4, a Full Synthetic fluid that is licensed worldwide and made by 40+lubricant companies including most of the big ones like Castrol, Ashland (Valvoline), and many more.
I pulled the fluid spec sheets for about half dozen of these ATF+4 and compared their specs to the actual MB 236.10 specs for the 'Bevo-List MB' fluids, and what do ya know, they match !?
I'm taking the Hot & Cold Viscosity #, Viscosity Index, Pour points, all the crucial specs, are identical.
We know the adage: "If it looks like a duck, walks like a duck, and quacks like a duck....."
So, that gives another option. I suggest you check around.
You may find the actual 236.10 fluid reasonably from a local MB dealer. Or they could ask $25 per litre
Me ?
Locally I can get ATF+4 in SuperTech @ Wal-Mart for $4.30 / qt
Or O'reillys ATF+4 in Gallon for $24.95 or Valvoline ATF+4 for $ 7 / quart.
Just did the fluid drain / refill + new filter / drain / refill on both e-wagon & ML.
The boxes shift & run flawlessly now. E-wagon had 45k on old fluid.
ML: ?? Looked ok but had to be sure, lots of towing + long highway high speed driving.
Of late I checked Amazon and they listed both Febi ATF and a new brand, Ravenol (the latter just made the revised MB Bevo list) as compatible to 236.10
My favorite Indie German shop here uses FEBI ATF exclusively.
Febi is a unit of Bilstein.
Anyhow, that's just some food for thought & what I've learned.
I just got done adding some larger upgrade tires to our ML, up to the larger size 265-70R17.
Next week I install the new shocks:
Front: KYB 349-226 Excel G (exact OE replacement)
Rear: SACHS SuperTouring complete Coil / Gas Shock (exact OE replacement)
Once done, I plan to tow up to the 5000# tow limit.
I'm kind of excited as this is my first time upgrading a Mercedes suspension.
Please keep us updated on how you fare.
Got any pictures of your Rig ?
Cheers - David in East Texas