[Don 95Vert]

I ran 123 MPH with my 4R70W and 373's and really didn't over-rev the engine - my rev limiter was 6200... You'll be fine.

You do need a chip to tell the EEC that the auto gear ratio has changed and to keep from hitting the limiter on shifts...

 

[Don 95Vert]

The car was tuned with SCT Software and the shift points were changed to 5500 instead of stock.

Do I still need to re-tune after I install gears?

Yep - A reburn just for the new gearset.