I was going by my own personal experience with what seems to me to be the exact same problem as the OP's, less than a year ago....I swapped tanks, checked hoses, and then next step, to me was to replace the regulator on the side that wasn't allowing furnace to stay lit. .I then did what Old Biscuit suggested, replaced the "red" regulator...didn't make any difference, in my case, still had the issue, but doesn't mean it won't solve your problem, was just my first "replacement" of components in my trouble shooting steps. But, .furnace wouldn't stay on...Next, and only component that I had not checked was the selector/regulator on the drivers side of my 5er...I replaced the assembly and it immediately resolved my problem..Thus the reason I posted my opinion..Guess it could be wrong, but sounds like identical problem and a possible solution to his problem...it worked for me.