When I put my truck in gear I hear a ticking noise. It doesnt make the noise in P or N... Any ideas? I have 155k

 

Welcome to the forum.
Sounds like broken exhaust manifold studs causing an exhaust leak under load. Pretty common. Look around the head/manifold area for black exhaust on the head.
If none can be found, check to make sure that you don't have a loose spark plug.

 

Awesome thanks! I have been thinking that myself. I just was not sure how to check. Would that lower my gas milage?

 

It may, all of the exhaust is not going past the O2 sensors and can mess with the air/fuel mixture a little bit.