Sounds like the flow restrictor(s) in the system have set. Turn the tank supply valves off and let it sit for 5 minutes or so to let the restrictors reset. Then open the tank supply valves VERY SLOWLY. Each spud (the male part that goes into the tank and regulator) in these LP systems has a restrictor in it. It's a small steel or plastic ball and light spring that is supposed to set if the idiots open an unrestricted flow and don't realize what they did. I've drilled mine out so my system is "unprotected" as I've made a decision to accept the risk knowing the issues in the system. Not for everyone but it works for me.
Pigman & Piglady
2013 Tiffin Allegro Bus 43' QGP
2011 Chevy Silverado 1500
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Street Atlas USA Plus