1994 F150 hard shift

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My 1994 F150 is shifting hard and nothing seems to be working like the 4x4 doesn't light up or go in to 4Wd the overdrive off light comes on but the truck still goes into overdrive. I'm told that the electronic shift control mod isn't working and the transmission is in some kind of limp home mode, any ideas on what i should check before i spend $1800 on a rebuilt tranny that I'm told won't fix the problem.