Possible pre ignition issue..

My 2009 Armada has for the last few weeks made a rattling sound when heavy accelerating or climbing a hill. It really only seems to happen around 2500 RPM and goes away fairly quickly. It does happen every time though. I also think it may be a little sluggish( but it could be in my head at this point) It idles fine(no rpm issues)
I have switched out to higher octane a couple of times with no improvements. I also have run Seafoam thru fuel tank. From waht I have been reading it sounds like a possible preignition problem. I am considering swapping out the plugs ( around 70,000 mi) My mpg is normal...

Any tips would be appreciated. Thanks