OK, I made the mistake of doing a search on the board for Dexron. Got extremely dizzy after the first page. Simply put, the dipstick says DexronII. The fluid I find at Walmart says for use where Dexron or Mercon is required. Is it good for a top off ('89 D250 with 727)?

 

Yes, it's fine.

 

When I put my Mag pan on, the instructions recommended ATF +3, which is now +4. Kinda pricy, but the truck is all synthetic now.