Whitrock fwiw I know it takes some front money or credit but if I were you I would get a tuned ECM, TCM flash tool, thermostat, and EGR delete kit. Then have the AEM done. After which swap in the ECM and send the original back to get your core money back. Flash the TCM and install thermostat and EGR block off plates. Now you have a far better running better towing and likely more problem free truck with a longer life expectancy than it currently has.
When you get your $3075 it will more than cover your costs and should be a great investment. Like most investments their is risk. It can still spit a bearing. In which case the tunes plates & thermostat can be carried to the next motor. 350k may go by without a hiccup. Naturally properly maintained. Make sure your ECM tune includes EGR cooler delete & turbo brake and it does not have to be a full delete so the exhaust & rest of the emissions stuff can remain intact.
The long cranking can be a couple things. Might ask member Haul n Grass. Mine was the lift pump. I linked rock auto. They have a factory replacement and an upgrade Spectra unit. I went with the upgrade and it’s been good a long time.
Badkoz you can wait on warranty expiration. I didn’t and have never been asked about whether I had a tune. I tuned at 30k and would do it over with a new truck. I would do it again only immediately after purchase if possible. Risks both ways pick your poison.