I have a 88 BroncoII and when driving one day I pulled away from the stop sign and I heard a bang and the thing stopped moving. I have line pressure and new pump gears the clutches and steels look brand new I also did an air pressure test to make sure the clutches were engaging and they were but it still doesn't move. Any suggestions

injectors are leaking like mad
so when did this old dog run perfectly>? last decade or?

I would think it is a plugged fuel filter/fuel line. The blockage moves away when you stop and then when you drive again it blocks the gas flow again.

would be nice to know the make, model , year of what ever it is
from your poor description , it could be a failed drive line shaft

That is a transmission issue, more than likely you need to rebuild it.

you have got some serious drivetrain issues but please inspect the cv axles to make sure there not getting hung up somewhere

Check u-joints on drive shaft.

broken cv axle??? were there any noises from the front end when turning for the previous months.

Sounds like you have a small bit of dirt or grit in the fuel system when accelerating it is drawn with enough force to cut off the fuel supply then is released when engine at Idle.
1 run liquid fuel line/injector cleaner in 1 tank
2 check fuel lines for debris
3 change fuel filters
4 have fuel tank flushed
here is trouble shooting order less expense to greater.

Very high probability an internal transmission problem.Check fluid level.Could be the torque convertor failed internally,or Low/Reverse band or servo.Remove transmission pan and look for any failed parts,metal chunks,etc..Scan for diagnostic trouble codes.Could hook a 0-300 psi pressure gauge,and do a line pressure test before removing pan.If line pressure is out of specification,internal problem.Good luck.