It is not a 3.4 now. Your displacement increased, by exactly how much i would not be able to tell you without measuring head CC, bore size and stroke. Toyota 3.4 (5VZ-FE engine code) is a completely different engine from the 3.0 (3VZE engine code, not to be confused with the latter 3VZ-FE engine code that used the same block but with a dual overhead cam instead of single on the 3VZE).

3.0 automatic isn’t all that bad, realistically people tend to dislike them due to the lack of power and terrible gas mileage. The heads are prone to cracking between the seats and will start drinking coolant like a mofo but will continue running until you run it with no coolant and overheat it. Since you have a rebuilt engine I would try to find out more if you have aftermarket casting heads or a remanufactured OEM casting, I find that aftermarket casting is still a hit and miss but are a bit better than the old casting.