After tranny oil change, tranny hunting for gears!

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I bought another 92 SVX pearly with 159K. I drained the tranny oil pan, removed the pan, installed new internal filter, put new gasket and bolted the pan back, added about 6 qts of Mobile Dexron III and Valvoline Dexron III, installed a Permacool external tranny oil filter (got rid of the OEM one), and installed a tranny oil cooler. Filter and cooler installation is correct, and have done so in my other SVX. But after doing the same on the new SVX, the tranny, after warming up, hunts for gears, lets loose, and sometimes shifts hard, and noticed that while idling in "D" the engine revs up a bit and then down in succession. How could I have messed it up?