2000 gmc rcsb 4.8. when i bought it the people said it was a stock 5.3. before i bought it i poped the hood and read the air cleaner box and it said 5.3. so i didnt think anything of it. but when i got home and look closer at the truck the sticker on the fan said 4.8. but the sticker on the air box said 5.3, but it said 2004 model. so i was pissed for a long time thinking they fu%&ed me on it and said it was a 5.3. but when i took i out to top it out and see what its got. it never shut off.so it has some kind of tune. and when i raced a few friends they said theyve never been beat by a 4.8. so now im thinkin maby they put the 5.3 in aftermarket. so how do i find out for sure if its a 5.3 or 4.8. and how do i find out what kind of tune it has???

 

What is the 8th digit of the VIN ? Look for the build sheet sticker in the glove box. What is the "L" code?

 

the only way its a 5.3 is if they put it in aftermarket. if it was origionaly a 5.3 the sticker on the fan wouldnt say 4.8. to only reason i think its a 5.3 is cause if they swaped the 4.8 with the 5.3 that they put the stock 5.3 aircleaner box on it and thats why it says 5.3 2004 model. and casue everyone says it runs like a 5.3

 

I can't understand half the things you type!!

Do what Mrgoodwrench3 said...

 

Just because its fast doesnt mean that it has a tune. Where did you buy it? I agree with Goodwrench check your vin number.

 

What are the numbers on the heads?

 

Someone could have swapped the fan also.

 

If it has a tune, u need software or a friend that has HPT, EFI L, etc.
To modify tune, at least. And that's hoping it's not tuner locked.

If in an accident, fan coulda been replaced, as airbox, heads or motor. Just a thought. Also, didja ever contact who ya bought it from? Ask em, hey, was anything changed that u know of? What's the history of this / previous owners?
Verify VIN as stated. Heads, ditto.

Stickers, air boxes & a fan can be swapped rather easily. Other things are a lil harder.
Heads can be changed. Internal dimensions (if stock) can be verified. A 4.8/5.3/6L have same external dimensions.

Lot of variables here. Esp. since you're not original owner, anything is possible.
Do some digging to find out. Or, Rock what u have.

 

Wow.

Anyway, I wouldn't trust the vin either as the motor can be swapped. The only real way to know is shine a light in on the pistons.

 

I said that. Other things can be changed too.