I'm still running the 7 psi carter pump on the frame rail that I installed in June of 2001 at 60,000 miles and I now have 240,000 miles on the truck. I had to replace the engine mounted 15 psi one at ~200,000 miles (it lasted 140,000). Prior to that I went through 4 engine mounted pumps in 60,000 miles. I've been very happy with the two Carter pumps in series.
YUP - I'd still be running that same setup, if it wasn't for all the hype about the "great Walbro" a couple of years or so back. I installed mine where the Carter 7 PSI pump used to be, but it and the remaining OEM Carter were still functioning perfectly, and I still have all my Carters stored away, just in case... :-laf
BUT, so far the Walbro has also proved to be just fine, and no problems or regrets on the install.