u/Guilty_Pension9576

I am new to train sim world, and I frequently come across a wired issue with my train. I play the San Bernardino Line most of the time, and when I play, the train starts slowing down for no reason. My breaks are fully released, Gen Field and Cab setup are on, Breaks are set to Cut In, Doors shut, And the train just slows down. I'm on a 1.0 down slope, Idle throttle, and I loose speed. I need help please.

I'm thinking about maybe purchasing it because I have no regional jets. Just curios if anybody does so if I buy, the aircraft doesn't feel left out.