duel fuel issues

Vz v6 duel fuel. Started running like crap on petrol but smooth as on lpg. Changed the plugs, coils and fuel injectors but no change. Any ideas on what it could be. Is there a sensor that might have failed. ? Any ideas are appreciated.

My 2003 VY factory duel fuel won’t switch back to petrol. When turning on ignition it is on petrol and idles fine however once I accelerate to around 2000 rpm it switches by itself to gas, then back to petrol for a few seconds then back to gas, if I back off it’ll constantly keep switching...