1993 Chevy Blazer Idle

I have a 1993 Chevy S10 blazer, 6cyl engine code "W". I had severe drivabilty issues with it and took it in for service, I was told it needed the central multi port fuel injector (octopuss), I had them replace it and they are now telling me that after doing that and also plugs, wires cap and rotor and also adjusting the timing that the veh still won't run properly under load. It will idle fine until you put it in gear then it appears to idle way down. They have no explanation $800.00 later. Any suggestions would be appreciated.