I'd get the trans-go shift kit rfrom Dave at tripleedgeperformance.com and go from there. That kit tightened up my trans. which now has about 2x the miles on it than your's and it's still running good. Replacing the plugs/wires didn't cause it, but could have made it more noticeable. Since you said there wasn't a lot of junk in the pan when you changed it then you should be able to make it live longer. Get the kit, do another pan drop/filter change while installing the kit and call it good. No fluid additives needed if everything is working right.
