I have a problem with a sprinter 311

Hello:

I have the following problem. I work in a workshop where we have a variety of Sprinter 311s, but I'm tired of taking the vans in to have them worked on and the mechanics not knowing what's wrong...
Well, the problem is that the fuel filter was changed because it was getting clogged. After that, the van wouldn't start anymore. We tried several times turning the key to try and get it to start, but it was useless. Eventually, it started and ran, but if you accelerate it to over 100 km/h, it stalls. I've tried the following things, but nothing works:

- I tried using a bottle and a hose to see what would happen, and nothing...
- We checked the relays, fuses, and wires, and nothing...
- This fuel filter has a sensor on the bottom, so we removed it and left it like that to test how it runs...

What do you think could be wrong with this van?