4 transmissions,none have overdrive

I have a 1989 GMC G2500 van and have in the last three weeks changed the trans 4 times and every time there is no overdrive.What can be causing this problem.The tv cable has also been replaced.Is there a control valve or computer that controls the overdrive? All the tranny's worked in the vehicals that they were taken out of.

the 700r4 or the metric200