Yesterday I walked down the street and I saw a huge dog. The dog was walking all by itself and I wondered where its owner was. Suddenly the dog starts running towards me at full speed. It's running so fast that I don't have time to think, so I jump behind a mailbox and watched it run right past me.
Opinion: I think we can use progressive tenses to avoid shifting tense. Here's the revision
Revision : Yesterday I walked down the street and I saw a huge dog. The dog was walking all by itself and I wondered where its owner was. Suddenly the dog started running towards me at full speed. It was running so fast that I wasn't having time to think, so I jumped behind a mailbox and watched it run right past me.