Toyota Repair: transmission problems, 1991 toyota camry, toyota camry

Question
Hi Ted,
   I own a 1991 toyota camry LE all trac which I just purchased last month.  It has 136,000 miles on the engine and transmission.  The previous owner replaced the original transmission with one from Japan.  The problem I'm having with this tranmission is that it stalls from 15mph to 40mph (feels flat with no power) periodically and the overdrive light flashes when it stalls.  When I accelerate from 0-15 mph it feels fine and then from 15mph to 40mph there is a "flat" no power sensation. There are no computer diagnostic code abnormalities.  The transmission mechanic says it may be an internal problem because this transmssion has 3  prong connector as opposed  to the original tranmission which has  a 2 prong electrical connector and can cause this problem.  Can you help me solve this problme?  The fluid is clean in this tranmission.
Thanks in advance,
Stan
slowed2@yahoo.com

Answer
I need to know exactly what connector the mechanic is talking about, if the transmission is not compatible or not the same as the original I can see where that can cause a major problem and is probably the reason the previous owner sold the car, I need more information, if the O/D light flashes the computer has detected some sort of a problem so I can't understand why there are no trouble codes, this makes no sense to me. It just doesn't sound right.