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Hi people. I'm new to this forum and hate to ask for help, but idk what to do. I purchased an older truck from an auction a few years ago. I hardly use the truck, but for moving gravel or quads, I just needed it since I can't do this with my VW bug. The problem started with realizing after I purchased the truck that there's been some rebuilding, and for a while now, I've been getting knock sensor codes (ie. low input P0332 and P0337). I changed them out last year with some lower end sensors + harness, but the codes returned, so I changed them out again recently with ACDelco and a new harness, and again the codes are reappearing. Now I'm wondering, although the Sierra 2500 (2006) came with a 6.0 vortec, is it possible that this engine has been swapped with a 5.7? I saw 5.7 written under the hood when I first bought it, but never thought much about it, and now I'm just not sure. I've looked on the front of the (leftside) head, but there was only a 4 letter code that didn't id anything. There were some numbers on the cylinder, but again, nothing comes up doing a search for them (ie. zero hits on google). I've heard that the engine number should be stamped somewhere near the rear of the engine, but I can't see anything. So where should I look for the engine's serial number? I know the engine is a vortec engine (as the plastic cover above the manifold indicates), I just want to make sure. If this is a 6.0, then maybe I will need to look at the PCM 'knock module'. If this is actually a 5.7, I think I may need to order different knock sensors (?) I'm not sure and could use some help. This is a picture of the leftside engine in front of the cylinder head. I think it reads D224? I'm not sure.