A lot of times our motors won't play well with aftermarket sensors and electronics. Search around for OEM parts on places like Amazon for cheaper than dealership pricing.

 

Rockauto sells

OEM Denso for 67.00 /ea

also

Delphi for 24.79 /ea
and Hitachi for 27.79/ea

I'd like to think either of the above are decent enough.

 

Check resistance on the coils, you can google search how to do this. You can also spark check them, pull the fuel pump relay, crank the motor and let it stall, pull plugs one at a time, put it back in the coil and hold the ground strap about 1/2" away from the intake manifold (wear dry leather gloves so you don't get zapped). Have a second person crank while you watch the spark to make sure it looks good, use one of the old coils for reference.

Slow cranking might also be indicative of a worn crank position sensor but since it happened right after you changed coils then you might have a couple that aren't working properly, especially since you bought some $13 coils...

 

Bottom line, "You get what you pay for!" If it's electronic or rubber I always stay with Nissan, belts or wipers and window motors or sensors!
Gary