i had a very similar problem about a year ago, your symptoms are the same as the symptoms/issues i was having. what fixed it for me was 2 things.
1. i reversed the TB coolant override, put it back to stock, i dont know if you have that mod but if you do its worth a try to reverse it.
2. i sprayed 2 cans worth of TB cleaner threw the TB and all the vacume hoses. had a sh!t load of white smoke coming out of my tail pips, i just kept spraying till it stoped.
i was told by a tec. that the coolant that goes threw the TB not only keeps it form freezing, but also prevents sludge build up because it makes the TB to hot for stuff to stick on to. i dont know how true that is im not a tec. , but it does make some sence .....