Doesn't cranck/ start

I noticed a few weeks ago that my Navi has been becoming increasingly hard to start. When starting the engine would turn over slower and slower. Yesterday morning I drove the truck 15 miles and shut it off. I attempted to start it an hour later, It turned over twice and stoped. There is a voltage drop. The lights dim every time I atempt to start the truck. I hear a single click from behind the dash whin I turn the key. I thought the problem was the battery. So I changed out the battery. Nothing changed. I need help! What could the problem be? My next step is to check the starter.

My next step is to check the starter.

Pay close attention to the cables while your working there.. many of these same problems lately were diagnosed to be dirty/loose connections.

I agree with Towncar! The starter connections can corrode and eventually break off.