Engine cuts out when slowing down.
 

1992 4.0.
I have this issue with engine cutting out instantly, like the electrics have been unplugged. Seems to happen when I'm slowing down at junctions, maybe at 10-15 mph, the engine will just cut dead. Thing is, it always starts up straight away and I can drive off no problem.
Battery is nearly new and alternator has had new rectifier, brushes and belt and been bench tested and ok too. One thing though, sometimes when I start her up, especially from cold, the battery light will stay on until I blip throttle a little then it goes out. Also, sometimes when idling in traffic, the voltage gauge will drop 2 or 3 volts, then pick up, or the needle will flicker quickly then appear normal again.
Any suggestions?