I have a 1995 Bonn w/3800 that I'm selling and the buyer said he smelled gas, well sure enough right up top by the rail was a leak.
Bought a new fuel line from the dealer and after install the pressure drops under load.
Keep in mind this thing ran PERFECT a day ealier, (except for a fuel leak) and it starts and idles with 42 psi until you put a load on it then the pressure drops off to nothing!

Any ideas???

I've checked and re-checked for kinks, changed the filter, scanned for fault codes, nothing there either.

Replace the fuel pressure regulator as it may not be working correctly now that it is getting full fuel pressure from the pump. Also check the vacuum line to make sure it does not have a leak.