will i get better fuel mileage with lq4 swap in 1990 pickup

I know this has had to come up, and sorry if it has been beaten to death, I have googled
and really have not found any solid answers.
1990 rcsb 350, 700r4, 342s, about 13 mpg. 358000 miles, almost broke in.
I have 2002 6.0, thinking about just a rebuild with flat top pistons, and I have a 2000 ls1
cam, do not have truck intake, I have ls6 intake with stock injectors.
My question is will I get much better fuel mileage?
If there is a good read that someone knows of or has any input I would appreciate it.
My first post ever so be easy on me.

you will, but will depend on your right foot. I can get 20-22 mpg cruising. 200k 5.3 with a manual trans

Thanks, Im on the fence, just rebuild the 350 or go 6.0. This pickup is not the toy, mostly a work pickup but I love it, I drive it pretty easy 90% of the time.
Its time for the engine to be freshened up, so if I could get better fuel mileage with the 6.0 I will go that route, but i have heard the 6.0 doesnt get
great fuel mileage

This is a no brainer. Do the swap. Youll be glad you did and wonder how you lived without it or why you waited so long. It really is that good. Im sure if you drive it sane it will at least match where your at now, but with much better power and drivability.
I was going to build up a stout small block before everybody talked me into the swap and I can say I sure am glad they did.

I appreciate the response, It wont take much for me to lean that way, I really would like to know if the 6.0 uses any more fuel, only 6.0 I have ever drove was a overloaded work vehicle, and the fuel was not out of my pocket so I did not pay any attention to fuel mileage, but I was impressed with how well it ran
for being so overloaded.

My bone stock 97 silverado with vortec 350 averages 15.5 city and highway combined. It will get almost 18 on the highway if conditions are right and I don't drive fast. My 06 silverado with a heads/cam 370 and 4.56 gears gets 15.5 down the highway and it's not a mild build by any means. A mild 6.0 with blow your 350 out of the water for both fuel economy and performance. No brainer in my opinion.

well that sounds good fast450ridr, why do you have such low gears? tall tires, or 1/8 mile runner? what trans do you have?

4L80e. It's built to race.

Go 6.0!! Honestly if there's nothing wrong with the 6.0 short block I wouldn't tear it apart. I have a ccsb z71 with a cammed/milled heads/stalled 5.3/4L60 and 3.42s, I avg 10 in town (because it's a brick with highway gears) and 16-17 on highway. I guarantee you won't regret the 6.0 swap

I fell off the fence on the 6.0 side, I sent a P.M. to beertestr for his mounts, going to get wire harness this next weekend, (hopefully)
then try to get harness all done, and order stuff to freshen up engine while doing harness, after harness is complete, freshen engine up.
Cant plan to far ahead I'm not that smart, so I'll leave it at that for now. Thanks for the replys Guys