I feel like a total retard but I cannot find the fuel filter on my truck. Ive looked up and down the frame rail in front of and behind the pump (where its been on my other vehicles) and cannot see it anywhere The truck is an 89 F150 2WD 5.0

 

It should be inline between the reservoir where all the fuel lines go (4 if you have a single tank; 6 if you have dual tanks) and the hi-pressure pump under the firewall. If there's no filter there, then it's inside the reservoir, and you MUST make sure you have a replacement O-ring BEFORE you unscrew the reservoir's bowl. It won't seal without a NEW one, regardless of the filter. I think the Wix/NAPA number for that filter is like 3333.