Why 1994 Thunderbird transmission will not shift to OD gears Acts fine out of OD but if in OD will not shift and becomes disconnected from transmission once throttle pressure released?

Bad news you need a new transmission. these were the first year type with o/d clutch pack instead of torque converter system. Simply put this is an internal problem complete rebuild.

I went through 2 of these both Ford OEM replacements the final solution was a Jasper Rebuild problem solved.