My shop said to replace the plugs since my current ones have been in there over 30k miles. I think I've had the +4s in there for about 35-40k along with magnacores. I wasn't going to replace the plugs until I got a CEL...or other symptom. I would do it myself and the shop knows it, so they wouldn't get any extra money off me doing it too soon.

So how many miles and what what should I look for before replacing my +4s?

 

No codes or any other running problems then dont worry about it, like you said they are just trying to get more $$$ out of you.

 

They know I'd do the plugs myself though...so they wouldn't get any more money...

 

I still would not touch it, cheap copper plugs will last 30k, Iridiums will last 100k, Platniums 60k, I dont have a clue on the +4's.
These are all approx of course.

 

I say go for it and do it yourself. Good preventative maintenance. If it was me I'd do it.

 

How many miles on your truck, have you replaced your plug wires yet?
Most plugs will give you at least 60,000 miles so don't worry about them, the wires would be my concern

 

truck has 142k. Installed +4s and magnacores at 100-105k