the big thing is are you useing synthetic or regular if your going to switch to synthetic is a little more smoother than regular type. i would use the synthetic mix then the next change full synthetic. if you have been using synthetic from the start you wont have any problems. i have been useing 5w-30 because i also have anouther car i drive as well the 5w-30 moves a little quicker than 10w-30 if you let it sit for at least two three days. it is mopinion and preference other than that it is up to you. ask put in 5w30 they will also see what type of oil as well. because i know majority of car manufacturers has switched to synthetic then the regular type my monte as well as my silverado and two fords i goof off with the manuels say use synthetic. plus my monte still has the warrenty has synthetic in it from the start. what i aam saying just keep tabs on what they use like you have been useing to keep a good record. i am actually impressed that your monte looks really good

 

I plan on making the switch to 5w30 for winter mainly to help with the cold start in below zero temps we get

BUT had the thought today, before I do anything I am going to look at my warrenty (5year 100k engine and trans) before I do anything and make sure this will not void anything,

 

the first number affects nothing. you can't be told you used the wrong weight since that number has nothing to do with oil weight.

 

Source that backs this statement please.