mine's a 1999, but yeah, the 4500 goes right in. aside from turning your stock crossmember around & changing the reverse switch, it's a direct, bolt-in swap.

it turns out the full-size nv3500s have 32spline outputs like the HD trucks, therefore your t-case already has the 32spline input & will bolt right up.
*disclaimer: i didn't personally verify this, but the fact that a number of these swaps mated right together either means A) it's true or B) there's some sort of witchcraft going on between the two units to make 32spline & 27spline shafts mesh*

the cross-over pipe coming off my left header is just a smidge under the pan, but it fits.

for your clutch setup: my engine's an '01 5.3, but i'm pretty sure the '99-00 4.8s & 6.0s both had the weird crankshaft length, so your current flywheel should work - get a disk & plate to match (LuK units have been fine for me). also make sure to get the slave that matches your current hydraulics (should be the 99-00 version). if it's relatively new & you need to save some $$, at least my '01 slave & flywheel part numbers cross-checked the same from the 3500 & 4500... but i just replaced both to be safe while it was apart (especially since my FW had ~150k & three clutches on it). make sure it gets bled GOOD (i'd recommend starting with a good bench bleed if you can)!

when sourcing the transmission, specify you need a late-model GM version (for the bolt pattern, internal slave, and synchronized 1st/reverse) - but ask for the earlier (95-00) square shifter GM lid because it's slightly lower & fits better in the 1/2 ton trucks without the factory body lift.

you'll also need an nv4500 shifter; the old one won't fit... and it has to be specific to the lid style (95-00 has a shorter pivot arm than the 01+). if using a factory-style shifter, your old stick will screw on to either of them, so you just need a base. i bought a whole setup from core shifters (pricey but good) after he got supplies to make some more, so Dan's old stock shifter (plus the new required spacer plate & bolts i had to buy) is just sitting in my garage right now...

and let me know how 33s feel with the 3.73s and a 5.61 first gear. i put 4.30s in 5yrs ago planning the cam and not 4500-swapping the truck... but then toasted the trans last fall & decided to upgrade on the replacement. now those gears are overkill, so i'm determining whether to put my old 3.73s back in or go down to 3.42s. not particularly wanting 3.23s or 3.08s because i've got a 219/224 cam that loses a bit under 1500rpm, and i do still pull a 5000-7000lb trailer occasionally & don't care for highway cruising in 3rd gear.

 

I’ll sure tell you if I get the swap done and have money left over for some 33s latest I’ll get the 33s should be right before hunting. Kinda curious why I would need to flip the cross member? Oh and such reverse switch do I need?

 

different longitudinal transmission mounting position. i just know that when i got the truck back, the passenger's side of the cross member (which has a slightly smashed bit on the outside edge) was on the driver's side, but it lines up with the bolts for the transmission... then i remembered reading that years ago in another guy's swap thread.

you need an nv4500 reverse switch

 

Thanks for clarifying, Just to make sure I need a nv4500 out of like a 99-06 2500 and a top cover off a 95-00 and the shifter handle I have will screw on?

 

I second the LUK clutches. When I removed the one in my RCSB after 30k hard miles it still looked great I saved it for a spare for my Tahoe which also runs an LUK clutch.

 

technically 01-06... the SUVs & HD trucks carried on the GMT400 platform through 2000
(yes, you could get a 21st century vehicle with a factory 350 SBC in it)

 

a couple models actually went through 2002 as square bodies.

 

...which got me to thinking. i just found a pretty sweet 2000 Z71 Tahoe with 104k. it'd make a great NV4500 swap candidate, too.
*squirrel*

alright folks, back to your regularly-scheduled programming

 

my nv3500 started with stock 3.73s & 31s
then bumped to 33s... followed by 4.30s (then technically a cam swap)
now the nv4500

my favorite driving feel of the bunch was the nv3500 with 3.73s & 33s. 1st was finally a little longer, and the rpms were around 2000 on the highway (gas mileage & my truck's always been really loud).

after doing more math tonight, i'm thinking 3.42s might be my ticket with the nv4500 & keeping 33s. compared to my 'golden setup', it's still geared a little deeper on the low end with a short 1st (good for trailering), but it's a little higher on the top end (good for the highway) and still sits ~1800: right above where my cam picks up, which beats using a 3.08 to equal out the old 1st gear feel but leaves me lugging the 5.3 in 5th. just FYI while i can't sleep.

 

While we are on this tangent I'd say 3.08s might be to much with 33s I'd go 3.42s and instead of re-gear the 10b just 9.5SF swap it with one that already has 3.42s.