I still think you have some issues to sort out if you are tryin to do burnouts but not able too, and a crown vic does do-nuts better than your mustang.
I myself was looking at DSS for an engine, but lately too many things have happened for it to be the owners fault, Imean all these engine have low low miles on them.
so DSS in my book=Junk.
Decide how often the car will be driven,and where highway or in town and your future plans for the car, me 4.10's best bang for the buck with the AOD.
And I'm glad you didn't loose your car after the accident I really like it.
Well I would start by, looking ever thing over like your drive shaft, u-joints, and rear end.
Do you know the last time the differental fluid was checked? look for any leaks, grab onto stuff move it around see if any thing is loose.
Definatley get the timing checked, a timing light is a must have if you plan on even popping your hood, and get a temp gauge they are inexpensive and easy to put it.
You should not be out flogging your car if you don't know how hot it is running.