I just recently bought a 1990 ranger with the 2.9l engine. It was parked for awhile before I got it. It did well the first couple weeks but now while shifting through gears it bogs down and will not accelerate. It so far eventually surges forward and goes normaly after a little bit. I've noticed it only does it if your shifting normally but when you run the rpms higher before shifting it doesn't do it. It has noticeably lost power in higher gears. What could cause this?