Could be timing advance is suddenly not working.
You might try advancing the ignition more at idle and see if it drives under load better and then retarding timing at idle if the advance does not improve drivability.
In the end, if that works, your distributor may need a new vacuum module or the rotating plate inside may be seized up.
Also, make sure that hose on the distributor is in good condition and connected. If the idle is too high, you might have a vacuum leak somewhere. Double check the carb. Is it seated solid or is there any wiggle to it.