Guys , do you have managed to find the problem. I have a similar issue , the forklift starts good, works fine for a couple of hours , and then shuts off. When i tried to start it again, wont start, it has good spark, and fuel.
I have noticed that when it won`t start, both of the LPG injectors are not working. So i think it is some sort of crankshaft pos. sensor. But i am not sure where it is located , is in the distributor itself ? Should i change the whole assembly ?

Ok. Looks like a teir 2 engine. I got it to finally start every now and then but will not idle up. It runs for a few seconds barely and shuts back off. I did get it to rev up once a couple times. Each time it will rev for about 30 seconds and then cut off them I can't get it to even hit again for a couple minutes. Have to let it sit. I've pulled both injectors and housing off and cleaned.

sorry I did not see that distributor was changed, is timing and firing order correct?

Just because your regulator is new, does not necessarily mean it is good, take off the 17 mm plug with a Phillips head, and check your lp pressure should be 5 psi, or 35 kpa if it is a newer Nissan that can be monitored through the meter panel. After verifying correct pressure, turn off the key and monitor pressure drop on your gauges to verify no leakage internal to the injector holder or its associated relief valve, also if you smell fuel coming from the air filter this is an indication of too much fuel pressure causing the relief valve to vent the excess pressure. If all that checks well check your basics, sometimes the slots in the distributor need to be cleaned off.

There are several vintages of that engine, does your engine have tier two or greater emission control system? More detail would be good, for example do you have good spark at the spark plugs?