Pausing in the bottom position will increase TUT - keep everything tight during the pause. However, you will probably have to use a lighter load in order to maintain rep count.
For speed I would always aim for a fast concentric and a controlled eccentric (once the loads are heavy the concentric will not be fast however fast you try to move the weight).
Getting a pump is much more related to metabolic stress, ie. if you do a high-rep set and a burning sensation in your working muscles, you will be more likely to get a pump afterwards. You would be more likely to experience this during 15s and 10s. During 5s it's a good idea to add a high rep metabolic stress set after you have finished the heavy work sets.
If you never get any soreness, increasing the number of sets seems like a good option to me. Try adding just one extra set and continue to do that each session until you feel like you are putting the muscles under tension for long enough.
Now might also be a good time to check on your form, to ensure you are throwing as much stress on your pecs as possible. Tris will always play an important roll in lockout.
