Rough acceleration, inconsistent idle

[rick1024]

Been having an issue with my idle not being consistent and the motor bogging lightly when accelerating. Sometimes the tahoe idles at 500rpm, sometimes at 750rpm and sometimes 900rpm. The idle is a bit rough. When accelerating sometimes I really have to put the pedal down hard to get it to move. There are times when it really feels like its struggling to get moving. Sometimes with light consistent pedal pressure it will downshift for no reason, but not at an alarming rpm where it could be damaging. Tahoe has a CAI from speed engineering, cat delete, canned tune from diablo (had the same issue without the tune) and just recently changed the spark plugs. Car has 175k on the clock. Any ideas?

 

[Fless]

Is the throttle body clean?
What does the MAF read in g/s at idle with a scanner? Is it close to the engine displacement?

 

[rick1024]

So quick update. I cleaned the throttle body, still doing it. I plugged my i3 in and changed the idle rpm to around 750. That fixed it, but every now and then while idling it misfires, just once or twice. Still has sluggish acceleration with new plugs in it. At times when accelerating it feels like its in too high a gear, when I floor it to get her moving it falls flat and then has a burst of acceleration when it finally downshifts. I am wondering if the throttle body is slow to react and thats what is causing this. Maybe the motor in the throttle body is toast or something. Also now there is a buzzing sound coming from the rear of the hoe, it only buzzes when i apply any amount of throttle. its completely silent when my foot is off the accelerator. could the fuel pump be going out?