transmission problem

[gsiemon]

I'm having a transmission problem with the transmission in my 94 Bronco (E4OD). After long periods of the transmission being in OD, the transmission shifts hard for about two or three days then goes back to shifting perfect, doesn't slip or miss shift or anything like that just shifts extremely hard. Seems like pressure is building up. Anyone have any thoughts, ideas, or had this problem? Any thoughts would be great.

Thanks in advance!!