Changed fuel filter today and after replacement my fuel pressure gage needle seemed to start floating. The needle would climbing slowly up to 15 psi then when i shut truck off, needle would slowly fall to 0. Do you think its air in the lines(mechanical gage no isolator)?

 

You do have a needle valve in line, correct?

Sounds almost like there is something stuck in-line there, air compresses against liquid the same (not thinking it's the air).

I would bet it straightens itself out after a few runs.

 

Yes i do have a needle valve, gage has been in truck for a couple years with no problems until today when i changed filter and wiped out the bowl.

 

I had the same problem and I ended up pulling out the filter and replaced it with a hastings, cant remember the brand I pulled out (GKI or something like that) was a huge difference in quality, but even with the new Hastings it took a couple of hours to level off, I think until the fuel filter media gets saturated it works against the lift pump

 

same problem, air in gage line, it cleared it self after a few days,

 

x2 same thing I experienced. Give it a few days or about 100 miles, sould be normal then. I don't drive my truck much more than 10 miles a day (work week) so I can agonize the change for weeks.