LS swap questions

[bodyman922]

I have an 87 silverado, 350 throttle body injected with 4 wheel drive I am looking to upgrade the engine in. The truck is a minnesota truck with usual rust and is used for the 4 wheel drive and the towing capabilities. It runs good but uses a quart of oil every 400 miles. I was told the motor has never been apart and has over 200,000 miles on it so I would like to upgrade to an LS engine if it is cost effective. I am thinking a 5.3 truck engine from a 1999 and up truck. I am not looking for more power only a truck that is more efficient. It would also help to keep another square alive!

I would like to know from those who have performed the swap if your fuel milage has increased or has stayed the same? Also would like to know if it is possible to keep the stock throttle body injection?

Any info you may have is appreciated. Thanks