Auto trans. 4-3 downshift problem

[rum runner]

1992 XLT ex-cab 4.0 automatic w/overdrive
156,000 miles
Regular service on transmission every 30k miles

Transmission drives out great except when going up a grade, it will not downshift from 4th gear; it only makes a coughing (or kicking) sound in the transmission

Any help will be appreciated
Thanks in advance

[2000mudder]

might as well rebuild trans cause you gotta take it all apart to replace the bad part.there is a overdrive module or a valve depending on what trans you have that goes bad.could also be chatter marks on convertor shaft from low RPM's in OD