lifter noise?

Hi everyone! I don't know the best place to post this so here i go. My 2001 Ford f-150 (185,000 mls) has a very noticeable ticking noise that accelerates when i give the gas. To be honest it sounds the same as an injector when you listen to it but you can here it with ease standing beside the truck. Since this started my gas mileage has dropped 4 miles a gallon. One other thing is when i floor it and after i let off and slowly give it gas again it will be missing really bad like my coil pack is bad but it smooths back out real quick. Any suggestions would be appreciate thanks!