Maybe the "5.3" you test drove was actually a 4.8 and you have it all backwards!!!

 

nah it was from the dealership, 5.3 was on the window. the guy was all tellin me i should upgrade to the 5.3 trying to get me to buy it. but i punched it on the way back, and wasnt surprised at all. i guess i can have it dynoed somewhere? that might tell me

 

how would this revel it?

 

Maybe looking for the part number from the crank or rods or pistons. Actually, since the 4.8 has flat top pistons, you might be able to pull a spark plug and see if you have dished pistons or not.

 

Look at the front of the block on the right side under the head behind the alt(also on the back left standing in front). The numbers 5.3/4.8 are cast into the block. One of them will have a big yellow dot on it. The one that doesn't is your engine ( I will verify this tonight just to be sure). This is not the most technical way of checking, but should let you know.

 

so how am i suppose to see this label on the block? i got down there with a flashlight and didnt see anything. i cant get my head down there far enough to see anything under the head