Ok guys I have a 1998 V6 4.3 vortec GMC 1500 Sierra truck . I have recently installed a 2008 V6 4.3 vortec engine, I am using all the same 1998 wire harness, sensors and intake manifold. All I am using is the block and heads off the new 2008 engine I have replaced the reluctur ring on crankshaft and crankshaft sensor with its original one (1998). truck does run but its out of timing, when I accelerate it responds good. but will not idle I have to keep foot on gas pedal to keep it from stalling. Weird thing about it, is that it will only run between #1 and #6 on distributor firing order. I have tried right at #1 where it suppose to be and does not run at all, I have already tried before #1, 180 degrees across, almost everywhere around and only runs between #1 and #6. Question is if anyone knows if 2008 camshaft is different than 1998 or is it ECU issue? if its ECU issue can it be manipulated to change timing on ECU since distributor is fixed on truck and cannot be moved? anybody knows if doing an ECU tunning will fix problem? I have already check for codes only code I get is something dealing with timing.