04 Silverado returnless style fuel system. Stock 200k mile fuel system. It's been idling rough and seems to be going lean at WOT. It threw a code for a bad FPR but I cleared it. And CEL came back on. And i havent checked codes yet. But It has a bad knock sensor I'm replacing today to rule that out. But any other way of telling if the FPR is bad? And can you replace the regulator on a return-less setup? I know its in tank. But will I need the whole sending unit? Or can I just replace the fpr. Also is the intank fuel filter replaceable on these truck? Any help is greatly appreciated thank you!

 

I think you might have to replace the whole bucket. The FPR and filter are the same piece if I remember correctly.

Put a pressure gauge on the rail.