Get the 6.0 - 100%
I drove my 6.0 suburban while brother in law drove his tahoe 5.7 (and later a newer 5.3 tahoe) on several joint family trips. Both only use 4wd. Mine loaded heavier every time. Mine beat his in mpg because I was using 60% Throttle and he is at 80%. Even when we ran 5 under the speed limit for one trip mine did better.
It is a longer lasting engine. It just wins every single category. I am a fan of the 5.3 and 5.7 but they just don’t compare to the 6.0.
His 5.3 did get 0.25-0.5 better mpg in city driving when both were empty, but he drives like a grandma and both my wife and I leave at the front of every stoplight.
How’s about I ran the last one only getting oil changes using normal valvoline at 30,000 mile intervals. Never new spark plugs or any of that. It passed its last annual smog with almost exact same numbers as when I first registered it with 30,000 miles on it. I regret letting that suburban go.
Then the fact that the 6.0 will have the 4l80e behind it. WAY stronger trans than it’s smaller brothers and no more expensive to maintain or rebuild.
I have heard that on the fly tuners can be used to raise mpg when just cruising. Idk how much that really helps, but maybe look into that too once it is all dialed in if mpg is the concern. I imagine tune would bump power also, but I would leave it stock that way. Plenty of torque to be in the front of the line anytime you want.
Disclaimer: have not towed with the 5.7. Did drive a few and they were Ok.
The 6.0 mated to a 6 speed slushbox is a nice combination and tows well. With a recent OE tune from GM, the '12 Burb I used got 10 mpg on flatlands with a 3.73 rear. Ran into somebody whom claimed 12 (rear unknown). Supposedly tuners can get better.
Only two problems with a 3/4 Burb that has the 6.0 and 6 speed: 1) GM decided that nobody wanted to buy them any more and dropped the line. 2) Used ones typically command a premium price and sell quickly.
While the 4 speed is known for handling the load, it simply does not compare to a 6 speed. Haven driven both in 3/4 ton platforms, the 6 speed wins for many reasons.
If the decision is to mate with the heavier duty 6 speed (6L90), had read where there was a batch with the internals installed incorrectly (IIRC O-rings) which showed-up as a 2 - 3 shift RPM flair. So just watch for what you are getting if buying used.
In general, you can't go wrong with the 6.0 gas motor. I had a 2000 2500 pickup and had several 5.7 and 5.3 Tahoes. Night and day difference in power. While the smaller motors are fine with a light load, when you put 4 or more people in or hook a trailer, the difference is pretty dramatic. That's why I drive the Duramax wherever we go if I don't need more passengers.
Omg !! no way would I have kept that. 14-15mph cuz my wife and I drive like a bat outa hell. Always first from light and freeway speed limit is 65 here, so 75-80 is more like it until the cops slow down traffic.
16mpg when we drove it like normal people drive.
That was for both the 99 and the 01. Infact, my 99 6.5 got 16 also. Thats what made the more expensive diesel hard to justify.
The b.i.l. With his 5.3 taboe and his 5.7 tahoe both had the cylinder shut off thing. They did 18 mpg and 17 mpg respectively, with only a person or two. Soon as you put any weight in them (like 4/5 people) he got 11-12 mpg. One trip we loaded about 200# and had 4 people that each weighed 250 # range and got 10.5 mpg for that trip.
My wife now drives a 2005 Escalade esv (like suburban not tahoe) thats full time 4wd with a 6.0 and it gets 15mpg this last 2 fillups, but I am having electric issue- think alternator is done at over 136,000 miles.
Last two years it has been constant at 15.25 mpg. Again, reminder of how we drive. And it is 80% freeway 20% city is my guess. The caddy is slower than the suburbans were and tad worse mpg- whats up with that? Emissions is my guess.
I will go along with the other guys, get the 6.0. I have never driven a 6.0 truck, but I have driven vehicles with the 5.7 and 5.3. If the 6.0 performs like these guys say they do, it would have to be an improvement over the 5.7/5.3. I have seen a 4000 pound camper make a 5.3 motor work real hard up an 8 percent grade.
On the other hand, If you were just riding around and not towing much weight I would say the 5.3 would be ok.
I'm guessing you're looking at replacing the existing 5.7l with a 6.0l? I ask because the 6.0l wasn't an option in a 99 k2500 suburban. Yes, the 6.0l makes more power than any stock 5.7l, BUT it does it at much higher rpm's. The 6.0l is a long lasting engine, but so can the 5.7l. Problem with the 5.7l us they had some problems and most people don't know about them or don't address them before they do harm. If you are doing an engine swap, then it's not a bad swap, but it isn't the easiest/cheapest out there. Some more details on what you're doing/after would really help answer your question.
Yeah, that was why I got rid of my 99- p.o. swapped the 6.0 into it. Everything looked clean and appeared stock. No clue what problems he had doing the conversion, sorry. I will will you that was why I searched out a k2500 with the 6.0.