You need to know why that SES light is coming on... This may point us in the right direction..
Almost seems as if you replaced a trans for what may have been a bad TPS... These cars are very dependant on the TPS for Engine load/Throttle angle which all serves as the kick down signal for the electronically controlled trans..
The 95 Bonneville uses an OBD2 connector, but it is a full on OBD1 system... You'll want someone that has a tool that can read the 94-95 GM'* with an OBD2 Cable...
Once you find out the code we can go from there
Also where are you located?
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