He's a gorgeous boy for starters. And you look very good on him. :)
He doesn't seem to want to drive with his hind end! Which gives you that just terrible wp lope. He also seems to me anyways, a bit tied down. Meaning- he seems to be scared to have forward motion. That's a big problem with a lot of WP horses. My horse came to me like that. I don't know what your trainer is telling you. But she seemed to be helping you with it. Also try taking your inside leg on him, lifting your reins and kissing.
He looks good at the extended trot but he could be a little bit more IMO. Always have a conversation with him not a yank yank [not saying you were doing that.] But don't just hold your reins and kick with your legs. Talk to him with your reins, just a little tug every once in a while. That will keep him focused and his nose tipped in. The loser your reins go the less you can extend, but the tighter your reins go the slower he's going to go. So try working on that a bit. Because to me he looks like he can extend more. :)