Spark knock?

[Damien]

I put a used engine in my '92 K1500 a few months ago and the engine had been running great. I think the engine has about 150K on it. Over the last couple weeks my gas mileage has been getting worse, about 10 mpg, but I figured this was because the temps have been below zero. The truck started idling a little rough yesterday and this afternoon I noticed the coolant temp was bouncing around between -32 and 190 degrees. About the time the DTC for the coolant temp sensor was set I noticed the engine knocking. I replaced the coolant temp sensor and the pigtail tonight, but now I have a knock that gets progressively worse while accelerating and during highway driving. If I shift into neutral and rev the engine its not there. I checked the timing and that seems fine. What else should I be looking at? Ignition module? Thank you for the help.