Does anyone know what changed from 1999 to 2000? I believe they went from 270 to 285 horse and can't find out why.

 

Just found it was injectors, is it worth it to swap in some 2000+ injectors and I'm guessing a tune will be needed with them right?

 

It wasn't injectors.

At one time they changed to high flow catalytic converters and also changed cams at one point.

 

PCM tuning mainly.

In 2000 GM was using 2 different injector sizes, manual transmission trucks in 2000 and all 2001+ trucks used the larger 25 lb/hr injector while all 1999 trucks and 2000 auto trucks got the 22 lb/hr injector.

1999 LM7 5.3 was 270hp/315 hp, 1999 L31 5.7 was 255hp/330 lb/ft.
2000 LM7 5.3 was 285hp/325 lb/ft.

1999/2000 4.8/5.3/6.0 cam specs
190/191 duration, .456/.465 lift, 114 LSA, 112/116 Timing

2001 6.0 switched to the 196/207 duration at .050 0.467/0.479 lift on a 116 Lobe center which was also used in the 01+ LS1.

peace
Hog

 

Thanks hog!

So I'm guessing just get the new injectors and tell whoever tunes it to update the tune for the 25 lb injectors and I will be in business.