Calling 9-1-1 to report an unmarked car attempting to pull you over and requesting a marked unit to respond would be the first step. Next would be to remain on the line with 9-1-1 and state that you were proceeding, with 4-way flashers on, to such-and-such at a slow rate of speed (say for the sake of discussion 25mph) with your interior lights on. Third step is to request 9-1-1 dispatch to contact the unmarked unit to verify their ID and advise them of your intentions.
Be prepared to punch the accellerator if 9-1-1 advises you that there is no unmarked vehicle responding. Leave interior lights on if you can, and proceed to your previously noted destination while telling 9-1-1 you are now moving rapidly and will not pull over/stop until contacted by a marked unit.
Do not exceed the posted speed limit unless things turn into a situationwhere you fear for you immediate physical safety (you get rammed, shots are fired at you, etc.).
Keep in touch with 9-1-1 dispatch until the marked unit arrives.
Remember that convenience stores are more likely to be staffed late at night than rescue squad/fire department stations. Not that the stop&rob clerk is likely to actively protect you, but they and their security cameras can be good witnesses.
But most importantly of all - think through, plan and at least mentally rehearse all of your plans ahead of time. (As an example, how many of you state your location address as the first thing you say when 9-1-1 dispatchanswers and asks "What is your emergency?" Why? Because you may become unconscious/unavailable before you can explain why you need an ambulance/police/fire truck and not all phones are E911 enhanced - especially if using a cell phone. By stating your physical address at least dispatch can play back the tape and send someone to find out what sort of help you were going to ask for. [Learned that the hard way. Got the address out and then became uncommunicative. Thankfully FD and rescue squad were co-dispatched and the FD carried a paramedic who was able to do lots of good/needed stuff before the EMT showed up.]