To create a 100 rated RB, set the upper and lower body 
strength low enough to put all the other stats at 100. 
Then, fill up the rest on your upper or lower body 
strength. 
The same can be done for a QB, TE, WR, DB, LB, DT, DE. 
However, for the LB, DT, DE, make sure they are big. 
For a DT or DE set the weight to 400 lbs. and height 
about 6' 0". For the LB, set the weight at about 260 lbs. 
and make him 6' 4".