My civic has no power and is eating up all my gas! what could it be?

94 civic LX auto w. a d16z6. so far its had a full tune up + brakes+new cat + new transmission in the last 3 months. but in the last week its been getting much worse, it feels like im hauling a heavy trailer, it has no power specially when im accelerating from zero. when im accelerating the rpm falls a little and the whole car kind of pulls back, as if im applying the brakes; eventho ive got my foot on the gas. there are no engine lights and the car ped CA smog 3 months ago. i took it to a mechanic and he took it for a spin and he says the car is definitely missing some power, but doesn't know what it is either. he says it would take more than a day to find whats wrong, but no promises. the car also gets terrible gas mileage, only 170 on a full tank! where do i look now? plz let me know if u have any info that can be hlpful, 10pts!!! thanks