Coming home tonight I go on to the skinny pedal pretty heavy. Watched the Fuel pressure drop from 13 psi down to about 7psi. Stayed in it a little longer and looked at the guage again and it had dropped down to 3 psi. Backed out of it and pressure only cam back up to 5 psi. Then I started nursing a little. after a few minutes the guage started bouncing back up to 13 psi and after a couple of miles it was holding steady at 13 psi.

Do you think it is possible to cause enough vacumn in the fuel line to drain the pressure guage line?

 

Doubtful. I have a feeling your lift pump is on it's way out.

 

Mine did that a few times back in Dec.. not sure if I have some thing in the tank.. or a piece of trash in the relief valve in the LP... it would act up only in the mornings.. and after about 30 miles.. it was back to normal... but I filled up with fuel once.. and that was the end of it... (not sure if it really had anything to do with the filling up or not..) but pressure has been fine ever since...
I figured my LP was on its way out... but its still going...

 

Im with BigBlue on this one .I saw mine do the exact same thing.
time for a LP

 

LP is on its way out. Some of the same symptoms I recently have dealt with...

https://www.dieseltruckresource.com/...251#post912251