Just put a new transmission in and now it has lots of power in reverse but as soon as it is put in drive it starts spitting and sputtering and loses power
My car has an automatic transmission.
Hello and thank you for your question. Sounds like the manual valve is out of adjustment and the transmission is applying the forward and reverse input clutch at the same time. This will cause the issue you are having.
You will need to check your linkage to the transmission to see if it is tight. If the linkage is loose, it will make the manual valve slip into the wrong spot making the fluid cross over to other circuits within the valve body in the transmission.
If you need assistance with diagnosing this loss of power, then seek out a professional, preferably a professional from YourMechanic who can come to your home to service your car.