If your owners manual specs Dexron 2, and the shop's service manual specs Dexron 2, use Dexron 2.
SP3 is a a higher spec fluid, and can be used in place of, or mixed with Dexron 2, in a vehicle spec'ed for Dexron 2. However, it's far more expensive and in your case, in a Gen 2.5, there's no...