Hi my name is XXXXX XXXXX Your complete satisfaction is my goal. Please provide as much information about your concern as you can.
Part # XXXXX Is not synthetic. it is DEX 3 relabeled as manual transmission /transfer case fluid.
Here is the description from the doc(NNN) NNN-NNNNdescribing dex lV when it first came out in 06
The content of this bulletin does not apply to manual transmissions or transfer cases. Any vehicle that previously required DEXRON®-III for a manual transmission or transfer case should now use P/N 88861800. This fluid is labeled Manual Transmission and Transfer Case Fluid.
If you want to use a synthetic, then use Amsoil, as J Hoop suggested. It is the best synthetic on the market.
There are two 6 speed transmissions that are available.
which one do you have, ???
Manual Transmission - Aisin AY6 Manual Transmission - Tremec 6-Speed
The tremec takes the part number you gave 88861800
the AisinAY6 takes
GL-5 SAE 75W-90 .
May be it would be a good idea to provide the VIN number to make sure of the application you have. That way option numbers can be checked to give you the correct answer you are looking for.
Or you can look at the tag on the transmission, Here are two examples
If you need more information, let me know.