Here is a pic of the top of my tank after taking off the bed. There are 2 different openings that I wanted to know if there were supposed to be hose attached to. Is it ok to leave it the way it is, or am I missing something here?

 

both of mine are the same way... I'm am also unsure of the answer to this question.

 

here is an excellent write up that shows everything in great detail.

https://www.dieseltruckresource.com/....html?t=151190

but to answer your question that is normal.

 

Another quick question. having read the "sticky" about it (thanks) the problem I had was the fuel tank gauge would read full, when I filled it, but after 40-50 miles, it would go straight to empty. I purchased a new sending unit and have installed it.
My queston is, arent the two halves of the whole unit supposed to slide, kinda like an according? Mine was in a jam and really doesnt move easily. Maybe this was causing the gauge to only read full, as it wasnt allowed to travel?