Death wobble

hi, we have a semi frameless dump end trailer Just had all new brakes on semi and trailer, new tires on trailer, but still have a wobble on the trailer wheels and also the steerling wheel shakes. any advice?

 

yes a 8300

 

not that we are aware of esp given as many people looked at it.

 

bare with me, my dad is the one that uses this one. But i guess we had this wobble for awhile now and he doesnt seem concern bc we only drive it when we sell grain, and haul turkey manture which both are a short distance and certain time of year.
When i was following behind him from what i could see which are just two sets of four tires on the left, the ones directly in front of the mudflaps wobble at 10mph, The right set, the two in front of the other two were really wobbly at 30-45 and i didnt see the left back ones wobble anymore. Then at 60+ they all seem normal. Now my brother would say they wobble at the front end bc he can feel it shake in the steering wheel. The trailer wobble is something i just noticed. If that makes sense.