I can tell you what I did to fix my T100 I sold it. I tried to locate the problem and found out quickly that I didn't have enough money to find the problem. I agree with AVERN I think this was some kind of glitch in some of the T100s. I have owned 4 and now looking for #5 I have always come out good on buying a T100 driving it for a year or 2 and then selling them.This was the first time I had one that shook like crazy and hope its the last.

Toyota T100 best truck Toyota ever built "Its so good the frame does not rust in half"