If my Ranger starts it is slow to build up speed, it usually takes about 7 miles to get up to 55 mph. Going up hill I have to downshift to maintain speed. Also it does not want to idle, I have to keep my foot on the gas pedal at a stop sign or it will die. If it dies I have to let it set for about and hour so it will start again. If I get someone to give it a push I can pop the clutch and it will start. It has had new plugs and plug wires and that did not help. It has over 200,000 miles.
Gotta do a plug and paste like mc, what maintenance has been done in addition to spark plugs and plug wires, ie air and fuel filters. Also in failure mode a fuel pressure test is advised.
A mechanic had this in the shop for 2 weeks and did every test he could think of. The only thing he could find wrong was it showed a vacuum leak but he could not find where it was. The truck has progressively gotten worse until it is now in its present condition.