2012 2.5i Outback - Transmission Problem?

I have a 2012 2.5i OB with about 123,000 mi on it. Yesterday, after leaving the base gas station and filling up, I noticed my car not shifting out of 1st gear. I let off the accelerator and then went back on and it eventually shifted to the higher gears. At first, I thought I had accidentally knocked it into manual. When I made it to the interstate I accelerated up to about 70 mph and started to hear a rattling sound as I was pressing the accelerator and the engine would lose power sporadically as I was trying to accelerate and there were no lights being displayed on my dash. I've had problems before on an older car with the intake and it not being properly fastened that reminded me of this issue. I pulled over and opened the hood to take a look for any loose or disconnected fittings and didn't see anything. I peeked into the engine filter box and made sure that was properly aligned as well. When I got back into my car, I proceeded down the interstate with no trouble or any light being displayed on the dash. I'm going to swing by the local car parts store to see if any codes pop-up.

Does anyone have an idea of what the cause is? I've had no troubles driving it today and prob put on about 70 mi on the car. Im worried it's the transmission but don't know if there's a way to tell besides jamming on the gas to see if it slips at all (which it doesn't).

Thanks