There is no such oil as Dexron 4, there is Dexron 6 (VI).
The difference between dexron 3 g and dexron 3 h is that dexron 3 g is used to be the factory fill quality. Dexron 3 g was the requirement for service fill quality.
Dexron III/Mercon automotive transmission fluid (ATF) is generally recommended as a replacement fluid for automatic transmissions meeting original equipment manufacturers (O.E.M.) performance requirements for current General Motors, Ford, other domestic and imported passenger cars, vans and light trucks where DEXRON II, DEXRON II-E, DEXRON III, AND Ford/MERCON fluids are specified.Dexron VI is a partial synthetic which properties exceed dexron III by 100% in every area. Dexron VI can not be interchanged or repalced with DEXRON II, DEXRON II-E, DEXRON III, DEXRON-III/MERCON.
Dexron 3 transmission cannot be used to replace Dexron Type A because they are not compatible. They are designed for use in different applications.
Better or not, really isn't the question. Dexron-II has been replaced by Dexron-III. Any transmission that used Dexron-II can now use Dexron-III. Fluids labeled Dexron-III/Mercon are also acceptable.
You can ALWAYS use Dexron 6 in any system that calls for lower number Dexron. You can NEVER use lower number Dexron than what the system calls for. I hope this helps.
Dexron III. You can Dexron, Dexron II, Dexron IIE, Dexron III, and Dexron V as suitable substitutes depending on availability. Lower numbers indicate a shorter lifespan of the fluid before you need to change it. Do no use Dexron IV (aka Manual Transmission Fluid) as this is likely to cause problems.
If it is a A/T Powerglide, you can use Dexron or a synthetic such as Mobil 1 ATF. You may not be able to find Dexron, but you can use Dexron II or Dexron III.
dexron 3 replaces dexron 2, so you could mix them but the dexron 3 is better
Trasmission fluid is Dexron 3.Trasmission fluid is Dexron 3.
Dexron III is itself an hydraulic fluid. The issue is, not all hydraulic fluids are equal in quality. General Motors recommends replacing the discontinued Dexron III with Dexron VI
Dexron 3 or Dexron 4.