has it done this all the while since you bought it or just started recently?
I'd be checking plug wires, plugs, ignition timing, etc if it just started.

Picking up a P30 would be a good idea, BUT the P30 also requires the knock sensor, which the car may not be wired for right now. it may require more work to get it to not throw a CEL on you.

Personally, I'd stick with your P28 and pick up a different chip for it. There are many out there, but http://www.hyperducktuning.com/ is one of the few I trust.
plus he has reviews on his site....
Mugen program: Dyno/Tests: Runs fairly rich, good power. Knock sensor disabled. Excellent program for all out power. On mild applications it tends to run rich.
I'd say for your setup the SuperChip program would work the best.
VTEC: ~5500rpm
Rev limit: ~8200rpm
Dyno/Tests: Excellent program overall, based heavily on Euro B16A program. Very simliar to stock maps with minor tweaks. 250-350miles on a tank without running lean on B16A motors and stock b18c motors (might require FPR). Does not work on JDM P30/P08 ecu. Knock Sensor disabled

I do not recommend the J's Racing program for the P28, it does strange undesirable things with VTEC on the highway.

if your P28 is all ready chipped, installing a different one is as easy as the five screws on the cover and pull out the chip and install another one, 10 minutes max.