LPG fuel supply problem?

I know this is an old thread but just hoping Fred or anyone can help.

I have the same van - LDV Convoy on an '02 plate,
I was touring the Northumberland coast in it when I ran out of LPG, I filled up at the nearest available LPG pump a bit further down the coast. There was no apparent problem for the next 40 odd miles, I was doing a lot of stopping & starting through the day, around the towns and beaches,,

Then it started to hesitate on acceleration, like there was a misfire.
It slowly got worse until it was unsafe to drive the van on gas (it runs perfectly on petrol).

Yesterday I had the injectors removed, cleaned and put back on. This appeared to solve the problem, at least while testing the system, but on driving away the problem returned, and got so bad that the van won't run on gas at all,, it starts on petrol, two seconds later it switches to gas (as it should) but no amount of throttle pedal can keep the engine running.
The system has a filter BEFORE the tank - but there is no apparent filter after the tank - unless there is one built into the tank?

I mention my holiday because I suspect the running out of gas brought sludge from the bottom of the tank into the system?? The van (and system) is 18 years old but has only done 50k miles.

I hope someone out there has more knowledge of these systems than I do as info seems so hard to find, and most LPG techs won't touch it.
Someone told me 'it's the fuel pump' 'in the tank', 'common problem on these,' but if the pump was shot, wouldn't it have given up completely? My pump has not given up, as was evident after the injectors were cleaned.

I guess my main worry is - Do I need to buy a new tank and if so, where from?

Thanks in advance for any help. Rory