i just recently got a 83 gt turbo and except for first and second gear if i try to accelerate and turbo kicks in it starts bogging down then will backfire if you try to stay in it. What could this be

I have tried
Ignition Timing
Remove Knock Sensor
New Vacuum Lines Removed original Cat Converter

 

so in 1st and 2nd gear you have correct boost and everything works but in 3rd 4th and 5th you have no boost?

 

Yes well the problem happens more so around 2 to3k revs well accelerating slowly into boost it seems to overload and then backfire unless you let off

 

Have you checked your fuel presure? Mine would do this when I had a leak in the fuel line at the pump inside the tank. As fuel demand starts to increase, the pump couldnt get enough fuel to the fuel rail and would start popping and missing. Put a fuel presure gauge on it and was fine at idle. As soon as you turn the key off, presure went to zero. Pinched the return line and still went to zero. Thought maybe a weak or bad pump. Dropped the tank and removed the pump and found the cracked hose. So umm yeah, check fuel presure