typical fuel gauge/instrument cluster question

So, I've been having a hell of a time figuring out what's going on with my fuel gauge .. when I got the car, the temp and fuel gauge were both inop. I assumed it was just the voltage regulator, but when I grounded both the gas and temp gauges, they went up as expected. I know it's common for the IVR to go bad, but I can't get any symptoms that are sure fire enough for me to take action on anything.

When I jumper the plug on the sender and the fuel line, the gauge slowly crawls up to about 3/4 full (before I lost patience - it might have went farther given more time) ... the sender was reading about 30 ohms with the *** end of the car jacked up (assuming it should have been lower, but 30 ohms should have still registered more than 1/2 a tank). At this point, I'm starting to believe it probably is the voltage regulator, but I'm stumped why the gauge operates when I jumper the sender ... is it possible that with a half-working regulator that 30 ohms is just too much? Any ideas or has anyone ever seen this before?