Kickdown

[JR1]

Maybe one of you guys can answer this question, my truck has th400 behind a 350, h052 in rear, when I drive easy it shifts at about 9 or 10mph and then at about 25 mph, if i get on it, its 16mph and 35mph, but if im above 30 mph and its already in 3rd i can floor it and it wont downshift, it just bogs until it goes into second at around 20 to 25, the camper does bog it on hills, is this a governor or something to avoid high downshifts...i had a mechanic check the vacuum and downshift mechanism on the tranny and he said it was good, can someone post a pic of the carburetor part of the kickdown, I've heard a th400 is a vacuum kickdown no cable but then ive read stuff about a carborator part of the system, this has a new carb so maybe part of the mechanism i missing

I at first put this on the wrong thread so I'm re poring here, thanks