Trans won't shift normally
 

Hey all. I've been having issues lately with my '04 GTO A4. It's got 3.91 gears, JBA headers, full Magnaflow exhaust high flow cats and all, which were installed before I bought the vehicle. It's also got a K&N drop in filter, B&M deep sump aluminum trans pan, and a Diablosport Predator tune. 87,xxx on the odometer. When cold, it drives fine. When it warms up, it holds RPM to about 3k under normal throttle, 2k under extremely light throttle before shifting. If I let off the accelerator, it'll force itself to shift. Strangely, once it's warm, if I pull over and shut the car off, then turn it back on, it'll shift fine for about 5 minutes or so and then start acting up again. Is this a torque converter lockup issue? It seems like some kind of electrical issue since it seems like it resets itself once the car is restarted. The fluid is nice and pinkish-red as it should be with no excessive debris. I've tried putting the stock tune back in with the tuner, and I get the same results. Any ideas?