Help please! 2006 L322 HDC and Transmission warning / fault

Hi

I have a 2006 L322 4.2 Supercharged that has been pretty much fault free for the last 3.5 years of ownership. It has done 63 000 miles.

About 2 weeks ago shortly after start up the dash display flashed up 'Transmission Fault' then something like 'limited gear selection' and 'Suspension Lowering', the warning dash light and traction control dash light then remained on. I switched the car off and re-started, after which the car was fine.

The next day the car flashed up 'HDC Fault' and the Suspension Lowering', again when turned off and back on the fault cleared.

Over the last 2 weeks the car has registered these same faults almost everytime its been driven (about 15 times), usually its just the HDC warning that flashed up but sometimes it flashes the Transmission warning and on occasions it has flashed up both warning one after the other.

I have taken it to a Land Rover specialist who ran a diagnostic check and could only get 'Module BUS' or similar, they said the ECU didn't seem to be talking to a module properly? They did a hard reset (what ever that means) but the faults persist.

I have replaced the battery yesterday (with a BOSCH 019 830Amp) but the car still flashed up HDC about 30 mins into my journey back from the garage.

There doesn't seem to be any pattern to the fault warnings - sometimes its within a minute of start up, other times its 40 mins into a journey cruising at 50MPH on the motorway (roadworks).

I have considered the following may be linked to the problem -

Car had an LPG conversion 2 days prior to these faults starting to occurr, this involved the battery being disconnected for 3 days and also the air compressor being moved from the spare wheel compartment, although not disconnected or anything and the faults don't seem to coincide with the air suspension being operated.

Car always sinks to its bump stops overnight, although it has done this for the last year or so (I intend to get this repaired in the near future)

Side bars were fitted day prior to the faults starting, although they simply bolted on and didn't involve anything being disconnected or anything

My thoughts/questions are -

Why did the diagnostic check simply show up 'Module BUS'

Is the LPG conversion likely to be the cause and if so in what way could an LPG conversion cause these faults

The old battery was the original one supplied with the car but when tested it came back 'Good Battery 87% charge' (I replaced it anyway just in case) - could it be something to do with the alternator, if so how would I check this?

What else could it be?

Is there anything I can do myself to try and diagnose the cause without sending it to the dealers who will no doubt want a few hundred quid to look at it!

Sorry for the long post but I wanted to put as much info in as poss.

Thanks in advance!