bowtieguy79

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3.42 have a set of 3.73's to put in at some point

cttandy

iTrader: (12)

My 89 has 3.42's. I got 21MPG with the stock P265/70R16's and currently get around 17 HWY with the 35's. On the interstate, it isn't real happy maybe break a whopping 15MPG.

With the stock trans, it would get maybe 18 or so. The mileage jumped up after having the transmission built.

How much do you think you can gain with the tune?

bowtieguy79

iTrader: (1)

Not really sure, but I'm hoping to at least top out around 17.5 - 18

Wife's Yukon is an 05 and it has 4.10's. Took it from Peoria, IL to Myrtle Beach this past summer and averaged 18.5 on the hole trip, best tank was 20.5mpg Run that tune on day to day driving and it gets 17 average around home. The 4.10's don't make it work hard at all

cttandy

iTrader: (12)

Have an experiment for you to try. Drive the Yukon 55MPH on the dot and see what you get. My 03 XL with 4.10's got 13.5 at 54, it got 13.5 at 56, but at 55 mph the darn thing got 22MPG. I thought it was a glitch in the dash read out so I verified it on a trip, came back with the same result. I don't take credit for figuring it out. My Dad borrowed it from me to take a trip. He came back and told me he got awesome mileage with it. I thought he was crazy, so I tried it. He said he put it on the instant read out and played with it until it maxed out, then set the cruise at that speed.

I pulled a trailer to pickup a jeep. I got 17 going down, and 15 coming back loaded. Trailer and load was around 9,500 lbs coming back.

For the record, if my wife drove it, she only got 9MPG.

bowtieguy79

iTrader: (1)

Can answer that, My folks live 40 miles away and I can stay at 55 most of the way. 21.5 is my best. 05 doesnt have instant read out for some reason.... 03 and 04 does..... 05,6,7 NOPE.... jerks...

Before I tuned it, you could see in the tables there where some sharp drop offs just below 55 at cruise conditions.

cttandy

iTrader: (12)

That is pretty interesting. I figured it must have had something to do with a "sweet spot" where the gearing and power came into play. I was curious to know what, if anything, was going on the tune side of things.

After driving both style trucks in lifted/stock/lowered, I think you will probably see a gain with the 3.73's with the taller tires possibly more with 4.11's. The TBI engines seem to like to be as low a rpm as possible as in 16-1800RPM at cruise, where the LS motors seem to like 22-2400 RPM at cruise.

victor3ranger

Looks like this post is a little old but I hope some of you guys might be able to get me lined out on some things.

I have a 95 GMC 4x4 that is all original and the motor is really getting tired so I figured that if I am going to spend the money I might as well upgrade to a 5.3L if possible.
I would like to reuse the transmission that is in it now if possible unless I somehow find a good deal on a package deal.

What are the specifics I will need to address to tackle this project?
Motor mounts? which ones and where to get them.
Fuel pump? which one and where to get?
Any change in fuel lines? If so what and how?
How to retain A/C??
Radiator?
Anything else?

I don't know squat about electrical stuff but I do have a shop full of tools, so if possible please dumb this down as much as possible for a newb to understand.

In the not too distant future I will need to do this for my 96 4x4 Suburban as well.

bowtieguy79

iTrader: (1)

Refer to post # 22..... and read my build thread here man, most if not all of the questions you asked are right here.

06murder

so doing an lsx swap in a 91 or so it have to cut the wires n stuff...n does it have to be tune?

bowtieguy79

iTrader: (1)

What are you asking?