I would leave the old motor in and have the LS built prior to install. Its really just preference though. Most tuners have a package to allow you to email them logs so they can dial the base tune in further. as long as you buy the apropriate tuning package you can do it either way with no difference. The only advantage I see is that if you should hit a snag in the build you arent kept from having a running vehicle until you fix the snag ny doing the build out of the truck.



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