jeep 904 auto issues anyone want to take a crack at this please

And I'm pretty sure it's a 904. When I got it and changed the filter and pan gasket I took them to the parts store. "A reputable one". And matched up the gasket and filter to a 904 which is what it also stated in his book.. What would be any difference in the other ones? I think I'll unhook the shifter at the trans and have my buddy manually put it in low to see if it still does it, that would rule out the mechanical part correct?