Dash clock resets when starting

I load tested my batteries last weekend due to a loss of voltage after the truck is shut down for a couple of days. I found the bad battery and replaced it with a new one. I tried to start it & it spun over easily but wouldn't start.
I snugged the battery posts again and it started no problem on the first try.
As far as I could guess the one battery post not making a solid connection to the ecm prevented it from firing up, to simple, but that easy. If I hadn't retightened that one post, a road call or tow would have cost a lot more.
Not to beat a dead horse, its worth your time n efforts to tighten all the connections that were loosened to replace your starter, including the batteries.

 

Always check ground connections! Definitely sounds like a bad connection.