Hyundai Repair: transmission, hyundai elantra, trouble code

Question
I have a 96 Hyundai Elantra.just put a engine in it everything works fine until it warms up ( about 30 to 45 min. of driving). The transmission goes from not going into gear to erratic shifting and starting off in high gear.at first i thought water was getting in the transmission because the fluid was a cloudy pink, but I checked and changed the radiator and flushed the transmission . but it looks more like the fluid is foaming up for some reason. and with the Trans dipstick out you can hear the fluid circulating . do I need to find another Trans. or is there something to do to repair the problem  

Answer
It sounds like your transmission is going into failsafe (starting off in high gear).  You should be able to get some instructive information by checking the diagnostic trouble codes in the engine and transmission computers.  
Anytime the transmission goes into failsafe, there should be a trouble code stored in the transmission computer.

It's possible you may just need a minor repair.