199 Blazer 4.3, 4x4 122,000 miles. Last December we replaced original engine with reman long block. New distributor, cap, wires, plugs, throttle position sensor, knock sensor, crank sensor. Last weekend replaced y-pipe, o2 sensors, cat and muffler. Still getting the p0135 code. Also before the engine is really warned up, it hesitates at shift. Will continue to hesitate until it gets good and warm than it runs like a dream. I'd appreciate any I'd ideas.