Try some trigger point releases on the particular muscle thats giving you issues. I'm having to switch my ultra wide stance squatting technique to more of a closer stance since I tweaked my hip last week. Deadlifting didn't effect the psoas much, but I know squatting will. So tomorrow will be working on the new form without much weight.
Good luck on the recovery and put heat on it and stretch!
- - - Updated - - -
Maybe your lower posterior chain and core isn't strong enough... Or maybe you're not engaging your core enough and its putting tons of strain on the lower back during the pulling.