Lost fuel avg

How exactly did they confirm this "leak", esp without removing the head?

Did they remove the top cover?

Did they inspect the exhaust valve on cylinder # 2? was it wet?

Did they remove the exhaust manifold?

How did they do it?????

 

Then I'm on the same page with @spsauerland below.

 

If @spsauerland is right, and that's an exhaust manifold then here's my theory.

Ask yourself this: What does a turbo do?

Answer: It pushes (rams) air into the intercooler (CAC), by using exhaust gas to spin the turbine.

What if the turbo is not operating at optimum setup, since the exhaust manifold bolt is broke ---> leading to some exhaust escaping before it hits the turbine?

Do you have boost gauge? What does it read, what is it supposed to read when you are at the "sweetspot"?

Since you've been experiencing power loss (as your butt-dyno would suggest), maybe you are overcompensating with the right foot --- as you said above, that you were passing all other trucks.

That may be why you've lost travel distance from 1200 miles down to 800, for the same amount of fuel.

 

You have a leaking/stuck open injector most likely. The added fuel has drpooed your mpg and caused that cylinder to run hot thus expanding the exh manifold and brake the bolt. The "oil" wetness is actually fuel mixed with soot. Do you have a pyro gauge on the truck? Guessing not. Sounds like you need to get it to a shop that can run diagnostics on it and confirm if the injector is bad or not and if it is hopefully they have a borescope to look in and see if the piston/cylinder are still ok and also remove whats left of the broken exh bolt from the head.

If you keep driving and passing everything in sight you will be needing a rebuild sooner rather then later.

 

Re-reading your post above, here's another arrow pointing to turbo/exhaust manifold

Light Gross weight = less load on motor = less boost = less sensation of POW-AH!!

Heavy Gross weight = HIGH LOAD calculated by ECM = MORE boost = YEEEEEEHHHHHHAAAWWW!!!