i dont know that much about transmissions but about the general quality of gm parts its not like it used to be where those were the parts you want for you car. they are now just what ever they can buy cheap and sell expensive just because people still have the mindset. they are no where near the quality of aftermarket parts you can get for half the price. i havent had to replace the original cat on any of the three cars 99 yukon 155k, 98 bonny 150k, or my 03 monte with 165k. but if one does go i certainly wont be getting one from the stealer.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock