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I'm in the market for a 1999-2000 Chevy Silverado Ext cab K1500 with the 5.3L engine. Since my budget wont allow me to purchase a later model with lower miles I'm still trying to find one with around 100 to 120k miles on it. So, when its time to pull it I have seen I can replace it with a 6.0L and get a tune for it. I would probably do all the normal stuff like headers and the MSD coil paks and such or can the 5.3L be given a stroker crank a new custom ground cam for more torque and add full roller rockers to it and still remain smog friendly for WA State?
Since it only rains here 9 months a year I will probably lower it to cut down resistance run light weight wheels and tires and keep it clean and waxed. Would I be able to maintain the near stock gas mileage with the 5.3 swapped out for the 6.0 or the stroker 5.3?

Yes I will keep an egg taped under the gas pedal.