First, front tank filling rear tank. Whats the part called, where is it located on truck? and is it an easy job? Second. Hearing a loud whining/ whistling noise coming from somewhere under and behind the cab....it only does this half the time and starts when i go over 25ish... truck drives the same but is suuuuper annoying. Anyone experience this? Lastly front tank doesnt read feul level. Pump works fine. Will i have to change pump to fix?

 

Can't tell you much without any details. I can't see what year your truck is from here.

 

Oh my bad guys. '96 xlt 4x4. W/351

 

Rear pump check valve is bad, when you run the front the back will fill at the same time. You will have to test the sending unit on the front tank to see if its working properly, you can test the pins with a Ohm meter. I believe its a dark blue and yellow wire and black wire.

 

Is the check valve inside the tank?

 

Its part of the pump, you can't fix it. Either you replace the pump or you buy the in-line check valve kit for your fuel lines.

 

Bummer any other insight to my other problems?

 

Well the whining/whistling noise could be exhaust related if you have holes. Does it get louder as you drive faster? Got holes in your floor?

And test the front sending unit like in the diagram above to see if its reading the right fuel level. Full tank is about 160 ohms and empty should be 15 ohms

 

The noise does get louder as i drive faster.

 

I'd start checking your floor and exhaust if its a whistling whining noise for holes.

If its a whining and chirping noise most likely a U-joint.

Grinding noise that sounds like an airplane taking off probably a bearing.