Bratt I have a friend with the same problem.
His problem (and probably yours too) is that he lacks strength speed. We both have similar speed at a barbell weight of say 225 lbs, but if you add 50 lbs, he can barely push out a single rep because he lacks strength speed, whereas I can maintain nearly the same speed.
How do you increase strength speed? Train with maximum weights. This is what ME day in WSB is for. Training above 90% using maximal effort, your barspeed will look very slow, but you'll be increasing strength speed, training yourself to lift a great amount of weight with the same speed later.
Unfortunately, my friend is a bodybuilder and doesn't belive training his bench above 90% has any place in his routine... but I gaurantee this is his problem.
Louie wrote a great (but somewhat confusing for beginners) article aobut this. Read it, then read it again in a month and think about how it applies to your training and it'll make more sense.
http://www.elitefts.com/documents/factor-of-time.htm
Think of it this way:
Gain in speed strength = able to push same amount of weight, but faster
Gain in strength speed = able to push a greater amount of weight, while maintaining same speed.
Dont' neglect one or the other, because they're both essential to continue gains. If you train only the speed str, you'll have great speed, but won't be able to do shit against heavy weight. If you train only for str speed, your max will go up, but you'll soon plateau and won't be able to do anything until you get your speed back up.