need help stalling
 

i have a 94 gt and it seems to start to stall at 4000 rmp i have checked the tps, have changed the fuel filter and have changed the air filter sometimes it will let the rpms go all the way to 6000 but that is if i whait a half an hour and i have to take off within a min or it will start salling again so if eny one have eny ideas tell me it would be great

thanx