Just having gone from 2.73's to 3.15's in my 2001 auto, I can verify that this is absolutely correct. Neither the shop that did the work (good local shop, not a Corvette specialist) and my locals trans shop thought the valve body needed replacement. The Trans shop did that and it didn't solve the poor shifting or P1870 (trans component slipping) code. Finally took it to a well respected local tuner (Certified Car Clinic, Santee CA) and he tuned it properly for the new gear ratio.
This was a two month headache from start to finish. Do yourself a favor - after the gears are in take it to a good tuner and spend the money to have it tuned correctly.

 

Shop that told me that was a highly regarded shop named Wheel to Wheel Powertrain. While no longer in business, most people have heard of them. Anyway, I have a totally stock 4L60E Transmission that has over 100,000 miles on it. The only mod was a 3200 stall Yank converter. For the last 50,000 miles, the trans has endured 2 different 427 inch engines yanking on it-The trans has never been apart, save for dropping the pan to change the fluid. W2W did tune the car for the larger engines, but the Yank converter was installed at 30,000 miles, while the original 346inch motor was still in place. From 30,000 miles to 50,000 miles, there was no tune done to anything, as far as I know, and the receipt only showed labor to install the converter. Maybe they did tune the trans somehow, but if they did, I was never told about it, and the cost for it (if it was done) was grouped into the labor charge for changing the converter. I stand by my claim that the A4 C5s do not need a tune to compensate for speedo errors due to gear ratio changes. You may be right as to the trans having to be "tuned", but as I said, I was never told about anything about the trans tune being changed. The PCM would not need a tune in the fuel/timing tables, which is actually the type tune I was referring to. But hey, I dont know it all, and dont profess to.......

 

bit late to the thread so I hope you can still get back to me, but what is that extra plate thing on the bottom of the 2.73 gears that the clean 3.42 gears don’t have? I am doing the same swap right now and worried the diff won’t fit since it is smaller compared to the one on the right. If you can get back to me I’d really appreciate that