no heat

1993 gmc vandura, 5.7 g3500, has new heater core, thermostat new hoses, flushed with brand name rad. flush. still not warm? do i shoot it or any ideas?

In case if its still alive and not shot! dont shoot it:) i wonder if its cold cold or warm when u say "still no heat" if its warm, i must say my does the same, it eventualy gets hot. My is 5.0L and what i know is that the heating on those vans simple isnt the best. They just didnt invest in it much, as they though most of them will be made for work purposes and must be not givin shit bout stuff like that as long as it heats a bit. Also, make sure ur thermostat u put it is OEM and will open at the exact fact specified temp rating.