can not get above 2000RPMs

i have a 1986 ford bronco II when i crank it, it seems to run fine and i am able to drive down the road at normal speeds but once it reaches normal temp. i lose all power it seems like and i cant get above 15mph and 2000rpms even when i park it and just rev the engine it will not get over 2000rpms it is not smoking and i have already cut the cat off to see it that was the problem and it was not any help is greatly need this car has stumped me
thanks

does it seem like is missing or cuttingout?