Here is a report on Remflex exhaust gasket that I installed on my 12 V 5.9 DP -For what it is worth.
I installed it when replacing a 14 cm exhaust housing back to 12 cm. I also had installed an ATS 2 piece exhaust manifold for a 2003 on up 24 v( to replace the stock one that had shrunk). I torqued and re torqued it to 35 ft lbs. The gaskets blew out at about 24-26 psi of boost. I'm not saying that it is totally the gaskets fault- an eroded exhaust surfaces- different exhaust manifold-Maybe not enough torque(not hardly) or too much boost(probably), may have cause this problem. Just making you aware the these gaskets failed for me.

On the way to Florida about 200 miles from here on the first big hill the " Remflex Burn proof exhaust gaskets" blew the rear section out on #6 cylinder- the motor would move the MH- but with no real boost. I had to drive 60 miles at max of 55 mph-to Phoenix to a Napa warehouse store to pick up stock gaskets(no one else had them)- they had 3 sets so I bought them all figuring to patch it up and replace them all in Florida- then drove out of the area to find a Wal-mart to install some to fix the leaking cyl.

Did some measuring and decided that 3 stock gaskets (The Remflex gasket was that thick compressed) would fix that #6 leak and since it was a 2 piece header- pryed back that section and installed the gaskets(stock is embossed steel)- tightened everything back up and went over all the header bolts again- so I sez- Ok- I'll change the rest when I get to Florida. Took off and everything was fine-- for a while until the next big hill- then she blew #1. So I sez- I'll pry that front section of the header off and replace all those 3 cyl gaskets and did- I doubled the gaskets because just one originally leaked some(before the burn and blow gasket)- Ok- that sealed that section good and boost is up and we are rolling.
The next big hill- you guessed it- #5 cyl blew!! I figured the end cyl were the weakest and that is why they blew- Nope- Just a bad gasket. So I finally did the gaskets on the remaining cyls and everything was fine from then on.- Shoulda done it the right way from the start!! We lost a day and half of travel time.

The the boost was up to 32 psi and the Motorhome worked fine after the stock gasket replacements.
P.S. I wrote to them and got no answer back.

 

I thought the Remflex was a one piece gasket?

 

Yes- it was. I had to scrape off each part of the gasket to install the stock gaskets.