When I bought my 2000, it did exactly the same thing.....pressure on the gas, nothing at idle, with accompanying chime tone and warning light. So I got a sender off of RockAuto, and my problem turned upside down, hahahah.
Now I have no pressure when I hit the gas, and great pressure at idle. I have a replacement sender to install.
I'll gladly report back with my pressure readings when I get a sender in it that works, LOL
1995 Jeep Grand Cherokee Laredo, 4.0L 2WD, 355,000 miles.