I've got a 2538 that I bought in 2017? or late '16. The only difference between the 2638 & 2538 is the 2638 has a better seat, and cup holder and power point. Other than that, the 2538 & 2638 are the same engine, power train, lift capacities, everything that matters mechanically is the same.
I've got 835 hours on mine, without any issues other than having the ECU flashed with an update, and replacing the battery. Dealer came to the house and did the ECU update at No-Chg. I think he "juiced it a little" cause I feel like I picked up about 5 hp.
I work mine hard. Built a house and used first 300 hours to move dirt, stone, trees, etc. Put the FEL to the max test. No issues. Most of the guys that don't have issues, are also very methodical in doing their maintenance as scheduled, or even sooner.
I was very close on pulling the trigger on a JD, until I sat in the 2538. It just "felt better" ergonomically, and the thing that won the coin flip for me is Mahindra's new engine doesn't require any BlueDef, or regeneration time for the exhaust system. That's was a big deal for me. The 2638 also has a bigger cu ft bucket than the competition.
Your dealer should fill the tires for you, as part of the deal. My dealer also raised the seat 3 inches and put a kill switch on it. I just happened to price a new 2638 last week, and it's $300 more than I paid for my 2538 a couple of years ago. Pretty good deal in my book.
Good luck and let us know what you decide!