As for the tripping, I would get his feet done first and then have someone watch as you ride him (or video you riding him). Some horses, especially those that have lived their entire lives on flat tracks or in flat paddocks, never learn how to pick up their feet and they end up as habitual trippers/stumblers. The only thing I've found to help them is to ride them a few thousand miles in country that requires they pay attention to where their feet are at...rough hills, deadfalls, things like that. Another part of that could be that he is still just incredibly unbalanced under saddle. The only solution for that is to make sure that you are balanced and then spend more time on him, asking him to use his body correctly.