Replaced the fuel lift pump on my Cummins ISL

Tom/Barb wrote:
Cummins lift pumps are reasonably easy to see if they are pumping. Disconnect the tank return line, turn on the key, if you get flow, it is working.

While this is a true statement, it does not tell you how much pressure you have in the system, as much as 120 psi at 2200 rpm. At various RPMs my pressures were all lower than they should have been by about 30%
hence the decision to replace the pump.
"Where was the air coming from ? the pick up?"
The only line I took off was at the pick up which was still very tight although I was able to tighten it slightly (less than 1/12th turn) before I took it off. The pits in the pickup were not deep enough and with a full tank of fuel should have been in the fuel.
Yes, it concerns me that taking off a line that was tight and putting it back on slightly tighter is what has stopped the bubbles in the fuel line at the second filter. I have not remove the clear tubing yet as I may still need to check for air in the system. Wish me luck. The only slight movement in this fuel line is at the pump where I could not find any sign of a problem.

*Why 5 hours to change? When I picked up the pump they said all I needed to do was replace the actual pump which is held on by three small screws to the base/bracket so none of the five lines would have to be removed. We did that and when powered up we had a bad fuel leak. Turns out the base was different and we have to put the pump back on it's base and install the complete unit. We spent over and hour trying to get one banjo fitting to start (using a mirror) and finally had to loosen the pump from the engine to get it to start.
In checking out this shop I asked if I would be allowed in it as I was willing to sign a Release of Liability. They said not a problem and I liked the attitude of the guy that worked on MHs.