'91 W-150, no overdrive after changing ECM

[Pootscoot]

1991 Dodge W150, 5.2L

After swapping out my ECM, I no longer have a 4th gear. 

My truck was overcharging (running at 17.5-ish volts), which burned out my headlamps and destroyed a battery.  A friend who works at Autozone said it was a bad voltage regulator, but according to Chilton, only the diesel engines had external regulators.  So I swapped out my engine controller and installed a new battery and headlamps.  It still ran up at 17-ish volts, so I turned it off and looked at the engine again.  I saw an external voltage regulator that someone had wired into the alternator and mounted to the inside of the wheel well.  I unplugged it and the truck ran at 12 volts.  I replaced the regulator at Autozone and it is riding nicely at about 14-15 volts**.  Unfortunately, I no longer have a 4th gear. I've tried pushing the O/D button in the cab to see if it would reset it, but it's still off. 

The new engine controller is a plug-and-play part, with factory imprinted data.  The truck runs a lot smoother, other than the O/D issue.  Is there a time/mileage I have to drive with the new unit for it to figure everything out, or should everything be working properly already?  It seems weird that the new unit would suddenly not be compatible with overdrive. 

Thanks in advance for any advice!

 

** It was suggested that the external voltage regulator was installed because it was a cheaper fix than a $168.00 ECM.  It was also suggested that I could remove the external regulator now that I had a new computer, but I don't know what it looked like before the previous owner jerry-rigged the wiring.

[Moses Ludel]

Pootscoot...Sounds like you have a 3-speed transmission ECM.  Check the part numbers and verify the ECM application.  You need an A518 application ECM.

Moses