I drove the truck yesterday and it behaved normally. I can’t explain why, but it appears the fuel filter may have been causing the issue. Or something gummed up in the fuel system that the cleaner helped work it’s way through.
I checked timing again this morning with the new filter and it’s 12.5 at idle and 9.9 at 2000 rpm. While checking, I found something else that was concerning. The upper radiator hose was stiff just after starting, which makes me think combustion gases are getting in there. I hope there’s no cavitation. I went to test the coolant and I think my test strips have expired. The DCA spot is very dark on all of them.