I aquired a 89-91 Ford Taurus from my grandparents earlier this year. I had to perform a motor swap on it as it had well over 250K miles on it, so I recruited my dad, long time mechanic and his shop to do the job. the swap went as planned. The weather is warming and I noticed it overheating quite a bit, so I stopped using the A/C and it seemed to help.

I replaced the thermosat... 3 times.
I replaced the fan motor as I thought there might be a short in it.
I replaced a control module (sorry for not knowing which one) that tell the motor to turn on the fan, etc. The part was used.

I cant seem to find the problem. Any ideas?

 

Assuming the coolant is full and the fans are working... I hate to say it but it sounds like it could either be a restriction (clog) somewhere in the system or a bad water pump. Water pumps aren't expensive... I got mine for like $30 from NAPA.