Rebuilt 350 turbo transmission stuck in third gear

If you can shift it into first or second and get no motion but it will move when you hit third the one two clutch pack is bad, the apply piston or the solenoid in the valve body is stuck. All three will cause this. What color is the fluid? Nice clean bright red? Were the cooler and lines flushed prior to install? Does not take much to cause a solenoid shuttle to stick.

When I put it in first manually the transmission will lock and skid the rear tires and putting it in first from complete stop the car will not move almost like I have my foot on the brakes, but when I put it in second gear or drive D it will take off in third gear and stay there. Fluid looks same color as when I put it in new two months ago. Reverse works but when you back up about a foot either the transmission locks or its rear brakes locking, I have put all new brakes on the rear, wheel cylinders and springs, but if you push the car backwards nothing locks, only backing up under power of the motor it locks. Thank you for your help!

Does not sound good. The locking is probably the stuck solenoid sending fluid into two different pistons at once, that is trying to put the transmission into reverse and first. Moving the selector closes one port off. Same issue when you select reverse. You might be able to drop the filter and valve body. Check the balls and solenoids for proper motion or even get a replacement for it. There are a few pressure checks you can make from the outside to verify the issue, do you have a source of compressed air and a transmission pressure test kit?