I have a 2000 Ranger 4x4 3.0 5speed. I purchased the pickup which had been sitting for 4 years because of a bad clutch, I replaced it and have been driving it for 20K miles and its ran fine. My issue is the pickup lost power at all RPMs and my CEL isn't on. The pickup idles fine and doesn't have a misfife. I've put a code scanner on it and there is no codes. I've replaced plugs, wires, air filter, fuel filter, and ran Sea Foam through the vacuum lines.
I had scheduled an appointment with the Ford dealership and the truck sat 3 weeks before my appointment, I regapped my spark plugs, and when I went to take it down it ran fine which is 90 miles one way. The dealer couldn't find anything wrong with it. Then on my way home I lost power again, so I checked my spark plug gap and they were where they were in spec. Still no CEL or codes.
Does anyone have any ideas or suggestions were I should start to look?

 

try checking your back pressure.its possible your catalytic converter is clogged. also try to check fuel pressure. another problem could be your mass air flow sensor. hope this helps.