What gets me about using amsoil transmission fluid is that it is a universal product reccomended for use in vehicle transmissions from ford to volkswagen and every manufacturer between. I have always been under the impression transmissions are very specific about which fluid they require and are built and designed around the fluid specifications. Or the transmission fluid is created and engineered depending on the requirements for the transmission.
Im fairly certain the OE cruze fluid used in the m32 transmission would not be reccomended in any other car manufacturer transmissions. How is it that amsoil is able to create such a universal product " compaitable " with im assuming more then 50 different transmissions ? What would you tell somone that feels more comfortable using a product specific for the transmission rather then a universal product ?
The fluids between vehicles are not as different as you think they are. They have the same base stocks since there are only a handful of companies out there like Shell and Exxon-Mobil that produce them. They have certain additives that they add to change the characteristics of the fluid, but the bottom line is it's still oil. There are some special cases where specific viscosities are required, such as certain Mustangs with a track package that need a 5W-50 oil, or certain Mazdaspeed 3 revisions that have an LSD with a clutch that needs a specific additive for the LSD to work, but otherwise, they are about the same.
If you walk into a store to buy some transmission fluid for your old truck, whether it's GM, Dodge, or Ford, it will be a universal ATF that meets Dexron3/Mercon/etc. There is no specific fluid for a specific vehicle. With the exception of CVT transmissions, the fluids are about the same. Each company has a minimum specification requirement for viscosity, oxidization, volatility, and etc, but at the end of the day, if the fluid meets those minimum requirements, it will be suitable for that car. DEX6 is the specification for the automatic transmission in the Cruze. It is actually a pretty good fluid from the factory being a synthetic fluid with a low viscosity and high heat tolerance. AMSOIL's Signature Series ATL meets and exceeds the DEX6 requirements, so there's really no reason to believe that it will not outperform the factory fluid and provide even better protection.
The OE fluid in the M32 transmission is horrendous. I have been wrenching on cars since I was 15 and I can tell you I have never in my life seen a fluid that performed as poorly as this fluid does in our transmissions. You might be able to get away with it with light all-highway driving averaging 50.2mpg with practically nonexistent stress levels on that fluid, but everyone else has experienced otherwise. Even the guys in the UK hate it. It is a weak petroleum-based fluid that cannot handle the heat and stress of the compact M32 under anything but extremely light driving.
That said, I recommend AMSOIL Synchromesh for the M32 for because it has friction modifiers that promote quick synchro engagement, it is the correct viscosity (Gear Weight 75W-80), it is GL-4 compatible as specified by the owner's manual, and it is a synthetic fluid. This allows the fluid to handle the heat of the M32 far better than the petroleum-based OE fluid (which by the way is ridiculously overpriced), it flows better (and allows the transmission to shift better) when cold, and lastly, it has a far higher film strength than the OE fluid, which protects the gears better. All this results in a fluid that performs excellently in the transmission, eliminating notchy shifting and either greatly alleviating or eliminating the 1-2 shift grind some of these transmissions are plagued with. However...that is my recommendation, not AMSOIL's. AMSOIL doesn't have a recommendation for this transmission, so it was up to us to do the research.
It is easier to understand if you have a technical background in mechanics and if you understand how fluids are formulated and what requirements components have. Your biggest concern with manuals is the viscosity of the fluid. As long as you have the correct viscosity, you could probably use any fluid you wanted to in this transmission with the same results as the OE fluid. Gears, synchros, and bearings are fairly simple components that simply need lubrication. Beyond that, you have antioxidants that keep the fluid from "sludging," rust inhibitors that keep components from rusting when the car sits for a long time, friction modifiers and anti-wear additives that protect moving parts under severe heat and stress (which add to the cost of the fluid), and so forth. Some applications require a specific fluid, such as VersaTrak fluid. Those are transfer cases/differentials that also have solenoid-based clutches. Most automatic transmissions, manual transmissions, engines, and differentials are not among the list of applications that require a very specific fluid. I said most because there are some exceptions. The Cruze Diesel is one exception. Since AMSOIL does not recommend any specific fluids for that vehicle, I will not either.
Historically, GM has made some questionable decisions with fluids. One example is recommending ATF in the C5 Corvette manual transmissions. Those owners are switching to a gear lube or synchromesh fluid for a reason. I know you have mentioned that you prefer to use the OE fluid, even though it costs you over $30 per quart. Personally, I have seen the results of the OE fluid as has everyone else on this forum and on four Facebook groups I'm a member of, and nobody swaps out OE fluid for more OE fluid. Everyone swaps in a fluid to fix the issues caused by the OE fluid, and those issues are very well documented.
If anyone mentions they have an automatic transmission (6T40), I recommend AMSOIL SS ATL because it will improve cold shifting, improve cold and short trip fuel economy, last them 2x as long as the GM fluid in severe service intervals (saving them money), and will be protected by AMSOIL's warranty. It exceeds the requirements of the OE fluid.
If anyone mentions they have a manual transmission, I recommend AMSOIL Synchromesh because it will improve cold shifting, eliminate notchy shifting, alleviate or eliminate a common 1-2 shift grind, improve shifting consistency, cost 1/3 the price of OE fluid, improve fuel economy (particularly in cold conditions), extend synchro and bearing life through superior protection, and last 4x as long as the OE fluid in severe service intervals. That, and it has been tried, tested, and proven in our vehicles by well into 100 owners.
There is really nothing special or specific about DEX6 automatic transmission fluid. It is used in almost all of GM's passenger cars regardless of transmission type and is listed as compatible in vehicles requiring DEX3. As a result, there is nothing product-specific about it either.