Truck running rich?

So I've been getting bad gas milage lately so I decided to hook up my scan tool, and I've got no codes, but my long term fuel trim sits at -14 at idle in closed loop and -4ish when I'm on it (-4 is the closest to 0 I've seen).

I got a code for my up stream O2 sensor a while back and I ran some "CataClean" stuff through (I usually do believe in snake oil cures, but someone I trust recommended it) and the code went away and the upstream 02 sensor is reading anywhere from .2-.9v while driving now.

My downstream is reading 1.24v flat so I think it's fried, but that shouldn't change the A/F ratio.

Any ideas on how to isolate my problem?

On a side note It does kind of have an airy ticking when under load, but I'm not sure how to test for an exhaust leak, which I think it might be.

 

The downstream only tells you if the Cat is working. The Upstream regulates your air/fuel ratio to the ecm. It can read fine or weird and still be bad. I changed mine out, just because of what I felt was bad MPG's, and according to fuelly, I've gained a 1.5 MPG.

 

That's what I thought. I think I might have a leak at my exhaust manifold, but I'm not sure how to test it