Hopefully someone can help me.

My cooling fan was not working so I replaced it myself. The fans now works. The problem is that when the car get hot but not excessively hot ,my Mazda begins to sputter and when I press the accelerator in will not pass 3000 rpm. I can cruise on idle but as soon asI hit the gas it starts to die. It will not shut off just not accelerate.
I had the fuel pump replaced but it didn't fix it. My mechanic can't figure it out.
When the car is cold in the morning it is fine. It will accelerate pass 3000rpm. If I leave it idle for 20 minutes the temp will go half way and the problem comes back.

Any help would be appreciated!!!

 

HAVE YOUR MECHANIC CHECK THE EXHAUST BACK PRESSURE; WHEN IT'S COLD AND AGAIN WHEN IT'S ACTING UP.
LOOKING FOR DIFFERENT WHICH WOULD INDICATE A PARTIAL RESTRICTION. ALSO HAVE HIM BANG ON THE MUFFLER;
I'VE HAD A VEHICLE WITH A LOOSE BAFFLE, ACT THE SAME WAY.