This one has me stumped. Here's the data:

Recently i'm getting rough acceleration (burbling/gurgling with vibration in the dash) from 3k-5k. Doesn't seem to affect acceleration, but it's definitely louder, noticeable, and substansial. The strange part about it is that on some occasions, I start the car and it's perfectly smooth... so it's occasional.

I suspected a possible exhaust leak, so I inspected it and had a few parts welded. Checked the aftermarket plenum for cracks and seal leaks, none present.

Could it be the car running too lean? May be occuring only when it's colder out (dense air). Other guess is it being related to issues with the tranny (lately having a hard time getting into 1st)

Any other ideas or things I should check would be greatly appreciated.

-- One more note is that my newly bought gtech unit reads unstable rpms below 4k (showing potential ECU issue) but WOT runs are recorded fine. Maybe all gtech's act that way?