Used cars import is for overseas Pakistanis only, and vehicles can be imported under personal baggage, transfer of residence and gift schemes only, and within these 03 schemes too, there are some conditions.
Now a days, used cars imports have become quite difficult. As far as I know, Bank Encashment certificates, money trail, tax return certificates, etc. are reqd. with Customs Duty paid from abroad in US $$$, and Bank Encashment certificate reqd. as proof of transfer of Custom Duty from abroad.
Sending used vehicle from US to Pakistan can be technically possible, but quite cumbersome and financially unfeasible. Import from Japan is the most easiest here, due to No. of reasons.
Rest, let experts here guide better and further.
I hope, all above helps. Thank you.