A little too much slack
 

My truck never did this when i got it and proceeds to get worse and worse my dad said there should be just a little bit of slack in the rear end but i have too much of it...when i go to get on the gas hard or let the clutch out it makes a weird banging noise in the back. anyway i can fix that? :disappoin

Grease the slipyoke on the front of the driveshaft.
It gets dry and binds.

my 2wd has a slip yoke i thought they were only on 4x4s

is the slip yoke at the front of driveshaft in the rubber boot ? if so how do you grease it?

You'll have to take the driveshaft out and seperate it to grease it. Get the grease from ford and mark the driveshaft where it mounts and also the splines. It is very important to line the splines back up where they were, it will cause a bind. If you reuse the metal clamps make sure they are tight , cause it will throw grease out of the boot.

if your truck is 2wd this probably doesnt apply to you, check for broken motor mounts, or place the truck in neutral, block the wheels and see how much rotational slop you have in the driveshaft