So I finished the 2.5 playthrough and I'm only on level 53. I am having difficulty getting more xp without being able to replay missions again. Any ideas for how to still get xp?
At that point I would progress to Ultimate Vault Hunter Mode (UHVM, or playthrough 3). The DLC that unlocks levels 51-61 also gives you access to UHVM.
If you really want to stay in 2.5, I would suggest farming for some useful equipment or killing BNK3R. BNK3R has a long initial run, but if you save & exit there, you start right in the area and it takes ~15 sec to get him to spawn.