99 Yukon 4x4 5.7 with 1345 engine code

[orange66fleet]

I bought the truck knowing it had some issues and fixed most of the except this 1345 code about cam/crank misfire issue. I have replaced the radiator, crank sensor, camshaft sensor, and passange oxygen sensor passed cat. All codes are gone but 1345. I read some of the guys having the problem replaced the distributor and or messed with the timing. If I start by turning the distibutor, what procedure for timing will I use. I have a adjustable timing light. Is there a certain rmp I time it at or is it at idle and what should the timing be originally. How long does it usually take for the light to go off. Sorry for the long post but, I want all the info down. Thanks for the help in advance and Happy Hollidays to every one. Oh, E-check sucks.