04.5 LLY turns over doesnt start

[Orange67]

Hey all, I've got an 04.5 Chev LLY CCSB with roughly 258,000 miles on the clock. Last Saturday it began to do a "hard" start- meaning I had to crank it longer than usual to get it to start, but not every time I started it. Yesterday after getting home from the lake, I parked it and the boat in front of my house and shut it down. 15 minutes later, I tried to start it, it cranks but doesn't fire at all. No SEL, no other running issues, just flat won't start. It ran great all the way to and from the lake, but I did notice when I started it up at the lake it took about 20 seconds or so to fire. I have read up on the "ice pick fix" for the injector connections, and tonight when I get home I am going to change the fuel filter, and look at a couple of harness issues I've read about, but mostly I'm at a loss. Any ideas or advice?