I just put in a used rebuilt engine that seems to run fine until upper 3rd, mid 4th and lower 5th. In 1st and 2nd, seems to rev fine, but in 3rd, seems to lose power at @ 5000 RPMs, in 4th loses power about 3500 RPMs and in 5th, no real power but slowly builds up providing there are no inclines...the only thing I can guess is possibly the tranny, with only 69,000 miles on it!!
Anyone have any advice/insight??
Gene and Dana

 

If its a non-turbo motor, the auxilary ports might not be opening. If its a severe loss of power, then maybe the secondary injectors aren't coming on.

 

Perhaps your car is just slower than you think it should be? You'll barely pull at all in fifth gear from low RPMs. N/As are slow

Could be your aux ports.

Do you have any other mods? Still have the stock catalytic converter?

 

A few additional things for you to check.

Compression
Air filter