How many hours are on the truck,has the regulator been drained of tar on a regular basis?
E-35 is LPG F/inj. open circuit malfunction
E36 is LPG fuel pressure sensor malfunction
E38 is LPG Vaporizor malfunction
Sounds like there is a bunch of tar in the system and the vaporizor needs rebuilt,what is your fuel pressure coming out of the vaporizor,should be 4-5 PSI
you need replace the lpg pressure sensor ,it is defect
Sometimes a faulty tank will show those signs.