Rough idle, uneven acceleration, loss of power- intake manifold gasket?

[speedmachine]

Howdy- lately the Tahoe (2004, 4x4, 4.8L) has been running a bit rough, seems down on power and accelerates unevenly...kind of wobbly or oscillating RPM when holding speed going up hills especially. Did the plugs and wires a few months ago as preventative maintenance and the old ones looked great. Idle after warming up is around 550 RPM. It feels like a vacuum leak of some kind. 260,000km (about 160,000 miles) and I doubt the intake manifold gasket has ever been replaced so I was leaning towards that. No codes or loss of oil. Any ideas would be appreciated, thanks.

 

[speedmachine]

Bump...also forgot to include that it wheezes/whines under acceleration right after startup but that subsides when hot.

 

[drakon543]

You can take a can of starting fluid spray it around the edges of the intake. Also give some of the accessible vacuum lines a quick spray. If the idle changes while you hitting a spot that's where the leak is if you do have a leak. Outside of that im not familiar enough with them to have any other advice.