I own a 1988 Ford Ranger extended cab, 2wd. 2.3l 4 banger. At 90,000 miles it has mostly sat for its life. I've replaced the front rotors, brake calipers, clutch, clutch slave cylinder, cap, rotor & spark plugs, all filters & fluids. It's developed a stumble after it runs about 10 miles or so. I...