Fuel pump????

[Kevin&Traci]

The other day as we were heading up the freeway, my L400 started to lose power like she was out of fuel and then just shut down. The Guage indicated 1/4 tank but I added 20 liter just to make sure and bled the filter. That got us going to the next exit about 1 km down the road and then it died again. I had a spare fuel filter with us so I swapped it out and bled the unit again. Off we go for another 2 km. Well, now the two easy fixes are off the list of possabilities. I bled the filter again and got another 2 km closer to home. Only 30 km more to go. I then tried just pumping the hand pump on the filter without cracking the bleeder and that seemed to do the same thing. I also found that if I stopped at about the 1 km mark and pumped it up again, it would keep running. Figured that would be much easier on the system. Finally got home a couple hours later.
Question is, could this be:
1) The spout filter in the tank?
2) Fuel pump?
3) Fuel injector pump? (or is that the same thing?)
4) A fuel component gasket?
5) Something else?
Any suggestions as to most likely possabilities and the easiest order of checking them, would be greatly appreciated.
Thanks
Kevin and Traci