Possible Misfire at 3.5-4K rpms?

[spikevyxel]

I have a 95' basically stock 240sx and over the course of the past 2 years i've had the car, there was occasionally a dip in power around 3.5 to 4K rpms. I kinda shrugged it off as a slight misfire, but since it wasnt very consistent i didnt really think much of it. This past week however there is a consistent and very noticable loss of power at those RPM's ranges. It seems to have happened the day after i took it to the track where it was pretty much raged upon. Seemed fine driving it home.

Any ideas or things that i should check please let me know.

Currently running Bosch Platinum +4... put in about 4 months ago.
91 octane
approx. 80K miles on motor

thanks in advance