I would like to know if I swap my 5.3 for a GM Performance 525hp 6.2 - do I need a new ECM or wire harness? I have the 8 speed trans

 

Which exact engine?

Link?

It's not that you need a new computer but you have to have it tuned. I doubt GM sells a tune that is just plug and play with an existing truck.

 

PART NO. 19369338

I have a mechanic who will do my tune - already have the TCU unlocked and ready to tune that as well

 

That part number is a fuel injected motor. It will Not be a direct drop in.
I believe your truck has Direct Injection

Look at the LT1 PART NO. 19328728 . If you want to bring it up to the same power level Just put a small cam in it.
Or the LT376/535 PART NO. 19355378 this has the GM Gen 5 LT1 hot cam and CNC ported heads.

The factory Gen 5 LT1 camshaft features 200/207 degrees of duration at .050-inches, .551/.524-inches of lift, and a 116.5-degree lobe separation angle.
The GM hot cam for the Gen 5 LT1 is 228/248 degrees of duration at .050-inches, .577/.577-inches of lift, and a 116.5-degree lobe separation angle.

 

If you're looking for a 6.2, I would be looking for a direct injected LT platform. That would pretty much be a direct swap aside from the tuning.

 

Thank you, the GM Gen 5 LT1 hot cam and CNC ported heads look like a good play - Thank you

 

Thank you!

 

your welcome! let us know how it goes when you get it done.