The biggest problem I see is a whole lot of advice being given without good information. Before you offer suggestions ask all the questions and wait for the answers. Right now at this point nobody has any clue what has and hasn't been done. Here are the Questions:
1. you stated it idles fine, now when you give it gas does the engine react as it should? IE revs just doesn't move, if it just doesn't move look annd see if the spur gear is turning let us know hte results
2. How far have you torn it down, and what did you do?
3. The biggest you can go on the Clutch bell is 17 teeth, the 19 on ups are for the Tmaxx I do believe the pitch is different on the 19 on up series also.
You can get great advice but you have to supply thorough information. We need to know exactly what your truck is and isn't doing in detail. Pics are also very helpful when your unsure of yourself.