F/P guage sending unit

I have the JR/Autometer fuel pressure guage.
at first after hooking it up I realized I had got a bad sending unit.
I called Autometer and they sent me a new one no questions asked, which was really cool. I got it in the mail and installed it and it worked fine for five minutes when my friend/installer was driving it. then it stopped working again. I called autometer and they said to run an ohmns test on the sending unit which we did.
it failed the test which means the sending unit is bad. we checked our wires to make sure nothing was grounded out and it is fine. any ideas?
I don't want to push my luck with autometer.