I just found a ton of free sheet music online (The Mutopia Project) most of it not trumpet music, but that's fine. I've been getting really into the Bach Cello suites and Violin Sonatas and Partitas, so I got all the music for those and read along with the recordings I have. Something I noticed is that I was tripped up in the big intervals where the music is harmonically based. I think we all develop a great eye for detecting scales when we're sight reading, but not necessarily other patters such as really simple things like dominant chords or inverted chords even. I know it sounds simple, but chord or arpeggio exercises will probably help your sight reading a lot.
If you see a C major scale in a piece in eighth notes, you don't have really read it, you just see it and look ahead because it's a given, just like we don't have to think of which fingers to push down after a few years of playing. That's the mental connection you're trying to build with sight reading, making as many things as possible as easy as pushing down three buttons.