2000 yukon 5.3 falls on its face

[Tahoeyukondenali]

We have a 2000 yukon as well as a 02,05, and also a 05 Tahoe z71, a 05 sliverado, and a 08 denali 6.2 awd. All but the denali have 5.3's. The wife's 2000 is a gutless wonder! It's running 3.73's with a tow package and only has 120,000 miles on it by far the least of any in the stable. It shows no codes runs fine except no power it don't miss sputter or stutter. It don't like to shift down unless you really crowd it and still no balls. Even the silverado crewcab with 280,000 miles with 3.42's makes the wife jealous every time she drives it. I thought about swapping the ecm from our 02 parts truck into it and see if it smartens up I've tried plugs wires coil etc. The scanner finds nothing wrong! I'm about to put a programmer in just to see what happens. That or I'm gonna take it from the wife and beat it till it goes or blows. Any ideas thanks for any help.
PS. the 08 6.2 awd denali is a beast anybody that hasn't strapped into one of these corvette suvs needs to try one mine is a rocket ship outa the hole and corners like my old bmw 325xi it's an adrenaline rush every time I fire her up it makes me feel like a kid again but is definitely gonna get me a pile of tickets

 

[SnowDrifter]

Post a video of a 0 to 60 run at WOT

 

[tom3]

You sure the wife's machine is a 5.3 and not the 4.8? But the 5.3 has only 10 more HP as rated that year. 9.5 compression with a 4 speed auto trans dragging 5000lbs. Run about forever but lots of changes in those motors since then.

 

[Tahoeyukondenali]

You sure the wife's machine is a 5.3 and not the 4.8? But the 5.3 has only 10 more HP as rated that year. 9.5 compression with a 4 speed auto trans dragging 5000lbs. Run about forever but lots of changes in those motors since then.

Of coarse its the 5.3 I ran the rpo but has the 862's for heads and she's got the 373's under it for rears. Its just a plain dog I wrote it off to the old lady that owned it prior to us babying it since it was new......"break them in like there gonna be run" theory which holds true around here if they drive 45-50 all the time they shift back and forth too much without a lot of clutch pressure internally and when a "hot supper" driver buys it it seams to have a lazy trans and gutless motor......break it in like its stolen off the lot and you tend to have a truck that can take the floggin day in and day out! But it should run somewhat like the rest the only difference motor wise is the heads except the now parts truck was the l59 not lm7 every other 5.3 has the 706 heads. Another thread had a weird shifting issue jumping to 3rd and not dropping back to 2nd and so far looks like mass airflow wich I never thought of but no codes so.......bout to but a diablo tuner on it max it out and hold her till she implodes cause I can't take the wife's 5.3 envy lol fact is I'm.tires of hearing it if a solution ain't found soon that's what I'm gonna do

 

[Tonyrodz]

Maybe someone swapped in a 4.8 in place of the 5.3. Afaik, only 4.8's came with the 862 heads.

 

[rockola1971]

Fuel Filter clogging up?

 

[Fless]

How much other regular maintenance has been done on it? Throttle body cleaned? Fuel filter, if it has one, replaced? What do the fuel pressure and fuel trims look like?

 

[Tahoeyukondenali]

Fuel Filter clogging up?

Replaced and swapped injectors....no difference so put the originals back in also new fuel pump

 

[Tahoeyukondenali]

Maybe someone swapped in a 4.8 in place of the 5.3. Afaik, only 4.8's came with the 862 heads.

L59's came with 862's as well as some Lm7's the only difference is the 862's are sand cast and the 706's are mold cast. I was never a fan of the 5.3 but had to learn to like them with the end of the obs yukon the 5.7 was more fuel efficient cause it had the power to haul the yukons fat ass around. Lol facts though with the 5.3 nbs I dropped from 18mpg to 11mpg and 11mpg is also what my 6.2 awd gets but that is all balls no powder puff. But seriously out of the herd of tahoe's and yukon's we drive regularly the 2000 nbs is a dog it is seriously getting the better of my patience I've had it checked out several times to no avail and with only about half the milage of any of the others we own it don't make sense in my head.....I can see the 05 with 4.10's having more nuts but less top end but the 05 with 3.42's and almost 280,000miles on it walking all over it makes absolutely no sense.

 

[rockola1971]

Compression check. 120k on a 2000 vehicle? Are you original owner or were you told stories? Not at all uncommon for these era K and C chassis to have instrument cluster swapped out and someone didnt get the mileage corrected. Look on back of instrument cluster for salvafe yard markings.