I have a '97 gmc yukon 4x4 with a 350. I have a p0430 which is bank 2 cat efficiency code. I'm going to just replace both. Figure the other 1 will be right behind it with 236k miles. What would be a good brand to use? Secondly my speedometer is reading 5 mph fast at higher speeds. I have what gm recommends on it for tire size. The speed sensor was replaced already last year when it threw a code last year.
I'm going to just replace both.
Why? Have you determined they are bad?
The truck is 27 years old. How much life could be left on it?
That depends on a number of factors, mainly whether the converter has been subject to abuse by conditions like misfires or oil burning. (The catalyst on my 27-year-old car is still fine after more than 370,000 miles.)
Given the cost of converter replacement I'd be ruling out the other possible causes for that code first.
First check to make sure it isn't the O2 sensors.
I have what gm recommends on it for tire size.
same rear end too? A lot could have changed in 27 years
All 4 oxygen sensors were changed by me.
The truck is 27 years old. How much life could be left on it? Some of the stuff was rigged instead of being repaired.