Truck 351w ..HELP IDLE...GRRR

I THINK ITS' AN IDLE ISSUE, if it could be something ELSE help out and say.

When i go to put my truck into gear its like the engine takes on too much load and dies. ...or... it peels out if i don't put foot on the brake it will peel out and take off.

*this is a 1980 truck w. a 1980s??? engine 351W

I checked all vaccuum liines, and brake booster, all are fine.
Checked and replaced carb gasket. Replaced Intake gasket.
Put in new plugs and wires, cap, rotor.
Distributor is in correctly with rotor at #1 at TDC.
Have messed with the timing forever
Messed with idle stop throughout everything....

I can't figure it out. ....any ideas... even random ones...

its an auto. ..but it only idles down to like 1000rpm... so i figured it was doing it cuz it wouldn't idle down enough to take the load off when its shiftd n to gear.
...soo, i can't find why i can't get the idle down...?

...tried similar with starting fluid, didn't idle up..??

what's propane do? same thing?