MCC-1776

I've got a 95 country, 2wd, 4.0L and I'm not sure witch auto it has. 176,000 on the OD. The problem I've had just recently is once it gets up to 3rd gear it doesn't want to shift back down again. I'll start from a dead stop and it will still be in 3rd I believe. I'll have to shift it down to 1st-2nd (all the way down) to get it going and then re-shift to D-drive. Sometimes this happens, and sometimes not. Checked the AT fluid and everything is fine there, good levels. So which faulty sensor is it? What wires have worn through, what gives?!?