i'd definately replace both. if i remember, the gmc's were about $150-$175
it's like anytime i have to put in a heater core or an evaporator , i change em both.
same with a washer & dryer.

good luck

Well so far it hasnt popped back up again.....Im not the type to ignore a problem but if its gonna behave itself, all the better for me! Like I said, no difference in performance when it came on so.....

If the knock sensors go out, performance won't suffer much, but I believe the ECM defaults back to the low octane spark tables for safety. So it's not a huge reduction in performance, but it is some. Also I believe even with the light on, it will only default to the lower timing tables if it is an active code. The light will remain on for 2 or 3 starts after the fault isn't present.

Yea Ferm it even did it after I cleared the code. I turned the truck off and re-started and erased again and no codes......Ive been about 20mi so far so good.....

Back on again.......Found my seal on the hood was open, thats prob where the water came in and went right into the "valley". Ironic that a valley captures water anyway and thats what they call it.....

CB and I changed my intake gaskets here in the yard. Looks harder then it really is! When doing it on the 4.8 you don't have to take the fuel rails off, so no messing with the injectors. Gound this out after, o well. But a easy job, and the knocks are right there when its off.