Running rich/ no power. Help

[NaturalGasForcedAir]

1996 305 vortec.
Under load the engine "pops" and has no power. It runs great at high rpms.
It smells rich/ very gassy smell. The engine has new plugs,wires,cap,rotor,fuel pump,fuel filter, oxygen sensors.
The truck is getting very bad mpg. Tried to plug into snap-on modis scanner, but couldn't connect.
Any ideas on the no power/ gas smell? no scanner connection?

Thanks.

 

[98_k1500]

No scanner connection is probably a fuse.