Unless you play a base 3-4 DO NOT only rush 3 players on 3rd and long.
I was watching the Clemson/GTech game tonight and was dumbfounded that GTech rushed only 3 on 3rd and long. I understand the thought behind it: more people in a zone means the zones are smaller. However, there are always holes in a zone and the more time WRs and QBs have to find that hole the more likely it is. Andrews called this garbage a bunch last year and it wasn't very successful (UM's conversion of 3rd and 16 came on a 3 man rush as did a long Clemson conversion tonight).
The problem is that you are basically allowing the offense to double team more than half of your rush. The person that is not double teamed is most likely your worst pass rusher. To be clear rushing three if you drop a lineman into coverage and rush a LB or DB isn't the worse thing in the world. It's even worse when the offense leaves a back or TE into block as now everybody is double teamed. The last Clemson play of tonight's game left the RB in to block. GTech rushed 4 meaning 1 lineman was single blocked. That lineman got far enough up field to spook a freshmen QB who then rolled to his right making the secondary's job easier. Of course Parker (the QB) threw across his body well short of his target and the game was over.
So, please DC's stick with what got you there. Oh, and I liked Mickey's nickel package of just completely swearing off lineman. Not only do you get a blitz but how is a QB to legitimately know where it is coming from.