CODE PROBLEM H E L P P L E A S E

I have a 96 dually with a 454. The truck runs great and will pull anything. The problem is after driving the truck for more than 30 minutes it will not start. The check engine light is giving codes 171
and 172 , right and left bank running to rich. After sitting the truck starts fine and off I go. The truck has 94k on it. I have been told it is fuel regulator, along with many other things. Cost wise, I would appreciate a guess if this is the problem. Thanks, Barbara
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I had the same codes but didn't have the no start problem. Checked fuel pressure, it was fine. Checked for leaking regulator by shutting of truck and found no decreases in fuel pressure after 10 min. Pulled egr to check for carbon build up, a sign of leaking injector plumbing. What I finally did, that fixed the codes, is have the injectors cleaned with Techtron (?). I guess if they are dirty they inject more fuel to get the correct power because it doesn't burn as well then the o2 sensor determines to rich and cuts the short term fuel trim. I know I was running -15 fuel trim before the cleaning and now only -6-8. 97 K3500 5.7

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