Need Help

[Tr95gt]

I have a 95 mustang originally v6 was converted to a 5.0 out of a 88 mustang its a auto but people who did swap went crazy cutting wires! When I first got car transmission was locked into forwars gears every gear except park the car went forward so I put new transmission in and car went into drive just fine but not reverse so I put it in reverse just left it in gear held brake and about 30 seconds later into reverse so I backed up then put back into drive and wouldn't go forward I'm lost on where to go and what to do next it's my dream car finally got it and haven't been able to drive it because of transmission stock aode all plugs hooked up on transmission modular hooked up help please I'm getting married on September 19 and my wife wants to leave wedding in my mustang