ive got an 04  silverado 1500 4x4. im looking for a 8 inch or larger lift system but cant find any. theres lots for the 1500hd, why couldnt i use one? any info to point me in the right way would be great thanks!  

There is a reason for this, it is very lightly built. A 1500HD is built on a 2500 chassis and has a 2500 front drive axle and suspension and a 9.5 inch 14 bolt rear axle that is a good bit stronger than your weak 10 bolt. I might add that it has same rear springs as a 2500 HD too. A far as I can tell, the only reason that 1500HD exists is for those that would never buy a 2500 truck even though it is one with a different label. Also the 8600 GVW of 1500HD lets it use the 2500's 6.0 too. Getting back  to you problem. You got the wrong truck for this. Some might figure out a way to do it but then have broken axles and very very short front suspension and ball joint life. You are better off starting with a 1500HD or 2500HD which has a much stronger frame too and also has after market kits for solid axle swap for front end. None exist for 1500 LD Silverado because of weaker design limitation of chassis. Sorry to burst your bubble here.