Which model is this exactly? Does the drum unit have a main charger cleaner on it?
I think i would try a new developer unit especially since wrong developer was put in it. Ive found those units start to get hard to turn around 400k copies and all it does is put wear on the main drive pack and it's much easier to replace a DV unit than a main drive
I would also check all the voltages in Sim 8 to make sure they match what the service manual says. Also make sure you have Sharp toner and put a new bag of Sharp DV in. If you don't replace the DV unit make sure it's very clean before putting in new DV.
What is the humidity like in your area? Is it extremly dry?
Blackcat your supposed to shake the bag of DV so you don't have to do extra stirs :P