Hello,
This is a known issue.
The transmission may have to be replaced, but it is probably cheaper to rebuild.
Also, the cooling system may need more extensive servicing than just a flush, though a flush should be able to take care of it.
This will need to be quoted with the vehicle present, and I would recommend using a transmission specialist.
From RepairPal problem reports - on found on this page:
The 2005-2010 Pathfinder with an automatic transmission may develop an issue which is commonly known as the "strawberry milkshake".
The name is based on the color and consistency of the fluid found in the coolant reservoir, transmission, and radiator.
The radiator on these models has an isolated portion for cooling automatic transmission fluid(ATF) that is pumped in and out by the transmission. This area of the radiator is known to rupture internally, and the following occurs:
Transmission overheating warning light
Transmission slipping (engine revs high and vehicle moves slowly)
Jerking when accelerating
Engine overheating
ATF and engine coolant mix in the radiator, engine, and transmission
Engine coolant in the transmission can cause severe damage, and if not caught immediately may require replacement or rebuild of the automatic transmission.
To correct the situation, the radiator must be replaced, and the engine cooling system must be flushed thoroughly. Also, the transmission will need to be professionally flushed, inspected, and possibly repaired or replaced.
To prevent this from occurring, proactive replacement of the radiator is necessary and recommended.
I remember this, it's these plus a group of Toyota trucks that had these issues for a few years. The good thing is it typically causes separation of the friction discs, and replacing those should not be as expensive as the transmission.
True, glycol dosen't damage the 'hard parts' directly - however IF overheating occurred due to clutch slippage - hard parts damage may be present .. A complete disassembly for thorough cleaning and inspection IS required .. Basically a transmission rebuild - including the latest applicable components upgrades. (That is the way I would approach this - if it were in my shop)