89 240sx bogs between 2500 and 3000 rpms

[madizm620]

my car has a new timing chain just put in and timing was done all at nissan, engine is basicly stock other then a cone air filter. For some reason it kind of lags/bogs when it gets around 2500 to 3000 rpms it's almost like it stumbles and doesnt want to pull like it should, as soon as its a little past 3000rpm it seems to run nice and smooth. Also i notice that when im gearing down to stop and i slow right down and put it in neutral the rpms drop real low for a second like below 500rpm, is this normal? any help would be great on this. and yes i did a million searches but did not find a problem exactly like mine. Thanks in advance

[Silvia2NR]

Did it do this before the timing chain replaced?

Any idleing probs? Cold idle probs?

[madizm620]

it was running like that before the timing chain was done and it doesnt seem to have any other idleing problems.