tranny issue?

So my 1985 Mustang has the factory AOD with a 2400 stall converter and I put 3:73 gears in the back. When I purchased the car 3rd and 4th gear were out of it. I had a tranny shop do a complete overhaul including a shift kit that shifts hard enough to break the rear tires loose on the 1 - 2 shift...

Firstoff this is my first time using a forum so I apologize if I'm pisting in the wrong place or I dont respond swiftly. I recently swapped a 289 into an i6 car with all the supporting parts, brakes tranny rearend EVERYTHING, granted it may have been a rushed job but in 17 and its my first real...