When should you change oil in a 2018 ram 1500 crew cab sport I had it since April and it's oct I only have 3500 miles on it

Hello, you did not state your engine size -- but -- Manufacturer's recommendation for your vehicle is "no more than 10,000 miles or 350 engine hours". Also, this changes dramatically to 4,000 miles if operated for towing or in dusty conditions (severe duty). So - for me: I would stick to the old 5,000 miles / 6 months interval for peace of mind. It's a great time to give the truck a good once over anyways -- twice a year. I know that automakers are trying to say their vehicles have "low cost of ownership", but to me, extended oil change intervals on most of today's cars just yield internal engine wear concerns that are entirely avoidable when considering an ounce of prevention.

https://carmanuals2.com/ram/1500-2018-owner-s-manual-110408