Please Help ..intermittent Trans Problem

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I hope that maybe someone out there can help me out.I have a 1995 olds acheiva 3.1 with 4 speed automatic trans.I have been having shift problems that I cannot figure out.It started when it would shift hard into 1-2 then hunt for 3-4 gears. The whole car would shutter as if it was stuck in o/d.So I dropped the pan and replaced the trans fluid and new filter and it did improve greatly.Now sometimes it will run and shift smooth as glass but then all of a sudden start acting up again.I replaced the fuel filter /pcv valve and checked all vac lines and connections and nothing seems out of place.The car will not throw any ses lights when it is acting up so I dont believe I can scan it for codes.I am at my wits end .I tried to disconnect the tcc selonoid and the car stalled like it is supposed to so that would eliminate that.What would you guys recommend that I could try or has anyone had this problem before??It is a 1995 olds acheiva s with 3.1 and 4 speed auto trans with 140k...Any help is greatly appreciated in advance.Help please this is my wifes daily driver...