Mitsubishi Repair: Possible tranny problem with 1996 mitsubishi galant (asian model E52A tranny F4A22), overdrive switch, mitsubishi galant

Question
When driving the car with overdrive on, anything a come to a stop & ready to move off it remains in the gear i stop in i.e it mostly 3rd speed. Hence it picks up slowly. I know this is not good for the tranny so what i do is i manually put it into low drive for a while then put it into drive and it changes okay.

The puzzling thing is that when the overdrive is off it works perfect.
If I am driving with the overdrive off & turn on the overdrive it instantly changes down into a low gear and brakes up ( you can hears the tyres screaming out there lifes)

Could this be a TPS problem (although CEL does not comes on) or valve body or clogged filter or tranny itself
I was planning to get a used tranny but would like to get your advice first

Thanks, Andrew

Answer
Andrew,
This does sound like a tranny issue, TCU, or bad overdrive switch.  Replacing your tranny with another one is a good first start.  If the TCU with the used tranny is in good shape, you may want to replace your TCU with that one when you replace the tranny.
Good luck!