[Impact1223]

I am looking at buying a 2008 Silverado with the 5.3l and when I drove it the truck felt sluggish. It has 305/70r18 tires on it and a leveling/ lift kit. Could this be why is feels slow to get up to speed or is there another factor?

 

[xPosTech]

Probably so, more so if it has 3.08 gears. The RPO option codes are listed on the glove box door. As for as tire sizes the factory size is located on the driver's door B pillar. This calculator will let you compare the sizes of the tires.

https://tiresize.com/tyre-size-calculator/

And thanks to Mike for the gear ratio RPO codes:

Also....Here are the RPO Codes for the Gear Ratios

RPO Code Description Ratio
GU4...AXLE REAR...3.08 RATIO
GU5 ...AXLE REAR...3.23 RATIO
GU6...AXLE REAR...3.42 RATIO
GT4....AXLE REAR...3.73 RATIO
GT5....AXLE REAR...4.10 RATIO

G80...LOCKER​

As Ted "xPosTech" Mentioned Above Here's the
Service Parts Identification Label and the RPO Codes, Located inside Your Glove Box

​

Ted