is it possible for it to throw off the speedometer when its changed? and how hard is it to change it yourself... is there any how tos?

 

are you talking about the gears in the rear end? if so then yes it can throw off the speedo. someone will chime in on how to change it since im not familiar with rears

 

Yes, if you change the rear axle ratio, the PCM must be corrected for the new gear ratio, or the speedometer will be off.

You need to provide basic info about your car - year, model, engine, trans and major mods. Not all years of the LT1 are the same. 93 for example needs the drive and driven gears on the trans output shaft changed to correct the speedo. Other year use PCM programming.

We can guess you have a 97 from your screen name, but why guess? Please add a "Signature".

Swapping gears take a bit of experience and several specialized tools like a pinion depth gauge and a dial indicator to check backlash. One tiny mistake, and the gears will howl loud enough to drive you crazy. If you have to ask how to do it, you probably shouldn't try.

Finally.... this is "LT1 Based ENGINE Tech" - engine related questions only. I'll move your post to the "Drivetrain" forum.