On the 1999 GMC Suburban, the P1345 is actually a very common problem on many GM trucks/SUVs with an 8-cylinder engine. The code is pointing to a fault withe Cam/Crank correlation. Most commonly here- the Distributor. There is a quick easy test for this. With the engine running, does the idle fluctuate? If not, shut the engine off and remove the distributor cap. Gently grab the rotor and try to rotate it left and right. I think you’ll find there is “play” when rotating it (there should be NO movement). This is a worn gear on the distributor and it’s affecting the timing (hence he cam/crank correlation). Replacing the distributor will solve the problem.
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