'87 Ranger

87 ranger has NO power going up a grade or hill. Idles fone and otherwise runs good except when you hit the gas it seems to hesitate for a scond and then takes off and runs great. Unless like I said before going uphill. Someone suggested oxygen sensor? Calalytic Conv. not clogged, new fuel pump, filter, plugs wires. Any suggestions?

Sounds like a problem I had with a 74 mustang II. It was a cracked valve. Do a compression test on each cylinder. If one or more of the cylinders varies greatly from the others, you know which head to pull. Replacement valves are easy to seat in but if the blow-by has damaged the seat on the head, you'll have to replace the head.