Where is the best place to buy a HD airbox? Mine has a broke corner and I like the looks of the larger filter in the HD box. I've been told that the gas models use the same one. Is this correct?

All the diesels use the same airbox. (HD and LD)
The difference is the years. In 1997 they went to the new style with the round filter element and it is a much better airbox design. The gas models use the same filter element but the airbox is different.

can you upgrade a 95 with the square filter to the newer round style?? Anybody looked into this before?

Yes, I did mine. The main reason I did it was because my truck has a body lift and the rubber hose tore. With the new style, I was able to rotate it down so it would line up.
The filters round filters are a lot easier to get in and out.

OK Cool So what did you have to buy and from what year trucks/sub/ can be used? Will Gasser stuff work for ours too or just diesel stuff. I be interrested in seeing what it takes for this mod.

My brother used to have a '96 sub with a 454 and there is no way that the airbox would have fit in my truck. The outside dimensions are a lot bigger and the hose comes out the side towards the engine instead of the front (toward the battery)
The filter is the same though.
If you get the hose and mounting brackets, it should be a direct replacement. I got mine from a salvage yard and it was missing the mounting brackets so I just bolted it directly to the fender well with bolts through the plastic.

i believe there is a different box for my 97. i bought a HD filter from napa and it wouldnt fit in my box, but the LD did.

I never heard of a different factory airbox. I would bet that the Napa book was just wrong. I tried buying a harmonic balancer from them and they tried selling me a pulley. Their books even cross referenced it to the GM part number for the balancer.

Why not ditch the factory airbox and use a round filter on a mandrel bent pipe? Like these dmax units I see. It would do a better job of flowing air and if you're worried about dirt and engine heat, cut the fender well open and fit it in with a box around the base.

QM, thats pretty much exactly what i'm working on for mine but doubt i'll exit through a hole in the fender, maybe just use the stock hole for now, don't know when i'll get it accomplished but will post pics of the finished product. I had a thought of using pvc pipe but have doubts it will survive under hood temps in the summer during shut down with the heat soak factor, i really don't want to suck in melted pvc through the turbo on start-up. Finding 3" mandrel pipe is giving me some trouble here and will also have to weld in an inlet for the tuna can.

Lots of good ideas here, thanks. Has anyone done any tests to see if the early stock air cleaner is more restrictive than the later one? And if an improvised after market one is better than the late model round one?