On my early 1999 7.3l I'm having a strange drop in rpms after the transmisson changes gears when under hard acceleration. After the shift occurs there's the obvious rpm drop due to the change in engine speed in the next gear. It's after about 2 seconds of the engine rpm's spooling back up under hard acceleration when it falls back in rpms. I can't see much of a change on the tachometer (maybe 100 rpms), but it's very obvious when listening to the engine.
I have no modifications except an hpx crossover and there's 200,000 miles on the engine.
Does anyone have any idea what the cause could be?