YEA I CALLED THE DEALER BUT THEY ARE NOT COMING OUT HERE UNTIL TUESDAY AND THAT WAS THURSDAY I GUESS I WILL JUST HAVE TO WAIT THANK YOU

I doubt that "resetting" the ECU would correct this problem, (that it stalls out after a few seconds running) but I would also recommend that you do have the/a factory trained tech come in and take a look at the machine to determine the actual cause or fault that is causing the shutdown.
While you don't give us a serial number to work with, I am pretty sure /it's my wild a$$ guess/ this unit's ecu will clear any codes if you disconnect the negative battery cable for about 30 minutes. but if there is still some reason the ECU is shutting down power to the LPG lock-off solenoid, the problem will return right away.

I HAVE A UNIT THAT STALLS OUT AFTER 5 SECONDS I CHECKED OUT THE OIL PRESSURE SWITCH AND EVERYTHING I COULD THINK OF I DONT KNOW IF I NEED TO RESET THE ECU

what is the real question you need help with? is the truck not running correctly, in what manner?

here is some help, this unit does not run when submersed completely in water, there is a need for air to get to the engine, so you will have to pull the truck out of the river before operation is possible. hope that helps.