It is more apparent when the car is cold but why whenever i shift at like 3500 rpm, does the car bogg down?

If i shift before 3000 it is fine and after 4000 is fine... Is it the "powerband" which my friend said but i dont know for sure.

Thx for any input
-Mark
P.S. is it cause i need new spark plugs?
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<span style='color:red'>- Conforti cold air intake
-Triflo exhaust
-Clear corners and tails
-Custom wheels
-Racing Dynamics stress bar
-UUC short shift kit
-Turnermotorsport Performance Chip
Soon to come - Zimmerman brakes, and suspension AND UMNITZA DDE IF I EVER GET THE GODDAMN MONEY

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