More ignition issues on the dart

if you can take your pickup back..by all means do it...but handy to have a spare. Trying tpo help remotely all we can do is suggest things from our own experiance... having had picksups go bad....and i'll guess at the junction between lead wires and the tiny coil....well you can see why they are sometimes the cause.

1 last thing as the whole lot all seems to work in isoltation (obvioulsy can't really test the igntion box)

try undoing, cleaning up with a wire brush and re doing up your engine to chassis earth strap...... couple of spikey washers and some grease on it will see it good for the next 50 years.. :)
this is an area thatb can just go bad usually after a transition from hot dry to cold wet weather or indeed humid to dry.. anything that has an impact on corrosion of the rust (brown) or verdigris (green and white) nature

resistance here will mess with everything.....

if there is a problem and you fix it you starter will spin faster as well...