4.8L to 5.3L Swap 2007 New Boby. Is it value added??

[nickhavlat]

I have a 2007 new body style 1500 crew cab short box 4x4 that has a 4.8L engine. It has 3.42 gears, limited slip rear, with an automatic transmission. I run stock 265/70/R17 tires on it. It seems to shift down more than I like to see during normal 60mph highway driving. I've had several trucks with 5.3s in the past and don't recall that much shifting due to power. Most of them had 3.73 gears though. I also only average about 15.5 to 16 mpg. My truck has 177,000 miles on it, so I was thinking about installing a 5.3 in place of the 4.8. I'm assuming I would have to have my ECM reprorammed for a 5.3 or buy an ECM from a salvage yard that was in a truck with a 5.3L. I also notice there are several different 5.3L options. The truck I have is not a Flex-Fuel. Does it matter which engine option I use?? Is the intake on a 4.8L the same as a 5.3L?? Can I use a long block from a 2001-2007 5.3L and install everything else from the 4.8L?? The reason I ask is because I have a 5.3L from a 2001 truck with 70,000 miles on it. Any help or suggestions???? Thank you!!!!