1990 5.0 Coupe wont run over 2000 RPMs!!!

hey guys. i have a 1990 5.0 5 speed coupe that will NOT rev over 2000 rpms after the motor gets hot. when its cranked the first time cold it will run perfect for about 15 mins till it gets warmed up. then it will completely fall on its face and wont rev over 2k no matter how hard you try to accelerate and will bog out and eventually die. then if i shut it off for about 5 seconds and restart the car it will run fine and will rev as high as you want it to for about another 15 mins. then it will do the same thing again!! ive tried to pull codes but for some reason i cant get them with either a code reader or a paperclip. im guessing this has something to do with a sensor like a TPS or PIP?

all help is GREATLY appreciated. thanks!

thanks! ive already tried a new MAF and cleaned the IAC and tb. but never even thought of the tfi. i also have a adjustable fuel pressure regulator that ill try. i think one of those will definately solve the problem!