35's on 2015 1500

I have a 2015 ram 1500 V6 with 3.21's and just put a leveling kit with 35" Cooper AT3's.

My problem is it never wants to shift to 7 and 8. I know that the truck thinks I still have the factory tire size so that causes some of the issue and that the tires are heavier.

I need to know what if any is the best way to solve or lighten the change.

So here are the questions I have;

Would buying a Diablo Tuner and PCM to change the tire size help any or will that just fix the speedometer issues?

Are there any other parts or things that I can do ?

Also I have searched through threads and found a lot of material but no that applies directly to my circumstance so that is why I am posting. If there is a thread that already exists I apologize in advance. I am grateful for any input you guys have.

You simply need more gear. Do you have the 6sp or 8sp transmission? And are you 2wd or 4wd?

I have 8 speed and 2wd.

Needs more than gears lol. Sounds like he needs more ass.
A programmer will do a lot of good. You will be satisfied even with canned tunes
And for sure get some gears. I'm gone say 4.10 no less than 3.92

Im in nearly the same situation and have been for about 6 months. Ive learned to live with it somewhat.
I have 35x12.50x20 grapplers with a 6 inch pro comp lift and 4x4.
I have the 5.7 with 8 speed. Ive learned to shift with steering wheel to 7th. That keeps MDS disengaged. Some times I place it in tow / haul mode but mostly ive learned to do without 8th gear unless im around 75 or 80 and that is very rare.
I have S&B and mufflex exhaust. Thanks to the steep gearing of the 8 speed its not terrible but gears are on my spring upgrade list.
A tuner will not let me adjust the 2015 model for a 35 inch tire so i have measured my speed /mileage with GPS enough to get an idea that my speedo is 2 to 3 off and that causes inaccuracies with my MPG indicator.
Gears will give you great results. I regeard my last wrangler tj to 4.88 with 35s it ran great around town just wasn't great on highway.