2007 Denali Oil Change and Transmission Question

[louisianadenali]

2 questions:

1) Oil change guy tells me I should ignore what the on-board computer tells me about engine oil life, and that I should do it at the recommended 3,000 miles on the sticker- I know this is just a sales thing, but my question is- with 114,000 miles how often should I change it, and what oil do you guys recommend? I have been doing a high mileage synthetic blend since I hit 100k, but have not gone full synthetic.

2) Oil change guy also recommends I get my transmission flushed and all new transmission fluid. 100,000 mile preventative maintenance also suggests this, but I have been told by some they don't recommend this unless you are experiencing transmission problems. I have experienced from time to time what feels like hesitation to engage 3rd gear.
- So do you guys recommend I get my transmission flushed and new fluids? I am currently putting about 1200+ miles/ month on my car due to work.

Any input welcome. Thanks in advance.

 

[kctyler]

I run full synthetic and change around 5k. 6.2L has 138k

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[louisianadenali]

I run full synthetic and change around 5k. 6.2L had 138k

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Awesome. Thank you.
What about trans fluid?

 

[kctyler]

I have not changed fluid..

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[Boyntonx2]

My 07 suburban that I had from 100k to 150 k had nothing but conventional oil all 150 k , I know because I had the full service records when I bought it, and all I used on it was conventional. Yes I changed the oil every 3000, I'm ocd though and do that with every vehicle I have, synthetic or conventional. when I traded it in at 150k, that 5.3 still ran like a top.