Low restriction air intake and exhaust. Duals aren't necessary, just go with a true 3" mandrel bent system. You can also port your MAF, that will help out too and it's free. Go to http://www.LS1.com for more info. Yes, that's mainly an F-Body site, but the 4.8 is a version of the 5.7 used in Vettes and F-Bodies. All the same tricks work.
Also check out SLP, they have a line of parts for LS1 engines.
You can also make better use of the power you have with a transmission shift kit and torque converter with a slightly higher stall speed. Yank and Precision Industries are two good ones I remember from my F-Body days. I had a 98 Firebird Formula with the 5.7 LS1.
Same thing with gears. What gears do you have? You might want to install a set of 4.10's, especially if you have larger than stock tires. The LS1 engines like to rev, so those gears might put it more in the powerband.
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97 Grand Cherokee TSi
4.0L Quadra-Trac
2" spacer lift
245/75R16 Cooper Discoverer S/T's
RE adjustable front track bar, OME SD40
Mopar skids and hooks
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