I've started work in a new lab for a month or so now but I've not been getting good resolution of bands >3kb in the DNA ladder. The lower bands are defined but those above 3kb are thick and smear. I was using TAE and tried 90V-120V. Higher voltage seemed to improve the resolution but still nothing as good as what I used to get in my last lab. Using new TAE didn't improve the resolution. I thought it could be the buffer, since I used SB in my last lab. However, I still don't get good resolution. I tried new DNA ladder, still no difference. I'm now wondering if the agarose is old (based on the batch no., it's 2007) and has degraded or changed in some ways (absorption of moisture?) detrimental to resolution. How long is the shelf life of agarose? Does old agarose give poorer resolution?