We often think of lifting as tightening and contracting. After all, how would loose muscles lift anything? Right? Wrong! The reason we don't lift to our full potential is because of an inability to get into the proper position for a particular lift. The back squat is the lift that readily comes to mind (even though the clean is way more obvious). In the squat, tight hamstrings and hip flexors keep the torso from being able to maintain an upright position (i.e. the proud or big chest.) You lean forward...good luck trying to get that weight up. So, what to do? Stretch and roll. I'll prove a point. The next lift day, do very small increments up. What I mean is on a 5x5 day, take a lot of warm up sets increasing 5-10% each time. You'll end up loosening up into the lift, and your lifts will get better in spite of the fatigue. Then, if that works, do some post lifting stretches. Long, slow stretching.
12 @ 65%, 8 @ 75%, 4 @ 85, 2 @ 90, then back down
KB presses 3 x 5 (heavy)
100 dball (20/16) slams for time