855 CUT engine dies after fuel filter change

So, I'm mowing long, flat, dumb & happy, when the Diesel engine on my JD Model 855 engine begins to sputter and loses power. It does this a few times and I recognize the symptoms of needing a fuel filter replacement. Did that. The filter I took out was pretty black. Then I opened the bleed screw labeled "A" in the operator's manual, it's at the filter outlet at the top of the filter, cranked the engine over with the starter and the glass encasing the fuel filter filled right up. When bubbles ceased at the bleed screw "A", I closed that bleed screw off and opened what the manual labels as bleed screw "B". It's right at the in-line injection pimp. When bubbles ceased there, I closed it off. The engine started up and was quickly running normally. Sounded great, no leaks, so I went back to mowing with engine running fine even at full speed. However, soon the engine sputtered and died. I went through the same bleed procedure as is outlined in the manual, and again the filter glass filled right up with the bleed screw open, and the engine started, quickly sounded normal, and I went back to mowing. Engine was running normally but again, soon the engine sputtered and died. I did the whole procedure again with the same result. The manual suggests cracking the injection line connections but I don't see how that can be the problem as it runs fine even and full RPM and developing good power, all-be -it, only for a short time, like maybe a minute.
What gives? I'm suspecting the mechanical low-pressure fuel transfer pump on the side of the engine. I don't think it can be the fine screen on the end of the fuel pick-up line in the tank since the filter glass canister fills so quickly with the bleed screw open. Perhaps the transfer pump works with the discharge pressure relieved when a bleed screw is open, but quits pumping when the bleeder is closed and there's some back pressure. I'd appreciate your thoughts, experience, recommendation.

Check to be sure fuel tank is venting. Check for good fuel flow from tank to inj pump.

Tx Jim, thanks for the back-to-the-basics reply. I found the trouble was that the "rubber" hose extending downward into the tank was in the throws of coming off the
steel fuel fuel line that comes down from above. After fiddling with it some, including blowing backward through the outlet line line from the transfer pump, I ceased to
hear bubbles in the tank. The "rubber" line had come completely off. Now there's a clamp holding the "rubber" line on and all is well. Not so tough after all.

Thanks for update & you're welcome
Jim