Trans Problem?

[jar2187]

While going about 45 mph, and then I get off of the gas completely the rpms drop from about 2000 just to 1500, and stays there until the truck starts to slow down to 35 mph and then from there the rpms and speed drop together until I come to a complete stop. Is this normal? I dont remember if it did this before.
I should also mention that sometimes when I put it into gear that the battery gauge goes down and so does the rpms. It almost feels like it is going to stall but it doesnt. What is causeing this?
When accelerating between 2000 rpms and 3000 rpms I get this werid rattling noise almost like metal flying around in a can or someting, is this pinging?

 

[MrShorty]

If it's an automatic transmission, then the RPM vs. vehicle speed behavior is normal.
The first thing I'd check is the IAC valve for the stalling when put in gear. It can get dirty which doesn't allow for free flow of air through the valve.
That is usually how "pinging" or spark knock is described.

 

[jar2187]

I just cleaned it a few weeks ago